(DOCS) (WIP) Define & doc resource manifest schema

This commit converts the type definitions in the
`dsc_lib\src\dscresources\resource_manifest.rs` file into a minimal
JSON schema. The schema represents the current state of the type
definitions, but raises a few questions for discussion.

The documentation for the schema is currently hand-authored and the
structure is experimental, since we have no official support for
documenting JSON schemas on the Learn platform.

For readability and referability, I recommend breaking the larger
schema up into smaller schemas and referencing across them.

Author: michaeltlombardi

docs/schemas/resource/manifest.md

@@ -0,0 +1,164 @@
+# Command-based DSC Resource manifest schema reference
+
+To be recognized by DSC, every command-based DSC Resource must have a DSC Resource manifest. The manifest must:
+
+1. Be discoverable in the `PATH` environment variable.
+1. Follow the naming convention `<name>.resource.json`.
+1. Be valid for the schema described in this document.
+
+The rest of this document describes the DSC Resource manifest schema.
+
+## Metadata
+
+| Metadata Key | Metadata Value                                      |
+|:------------:|:----------------------------------------------------|
+|  `$schema`   | `https://json-schema.org/draft/2020-12/schema`      |
+|    `$id`     | `https://aka.ms/dsc/schemas/resource/manifest.yaml` |
+|    `type`    | `object`                                            |
+
+## Required Properties
+
+The manifest must include these properties:
+
+- [manifestVersion](#manifestversion)
+- [type](#type)
+- [version](#version)
+- [get](#get)
+
+## Properties
+
+### manifestVersion
+
+The value of this property must be the semantic version (semver) of the DSC Resource manifest
+schema that the DSC Resource manifest validates against.
+
+```yaml
+Type:     string
+Required: true
+Valid Values:
+  - '1.0'
+```
+
+### type
+
+The value of this property must be the name of the DSC Resource in its namespace. This value must
+use the following syntax:
+
+```text
+`<owner>[.<group>][.<area>]/<name>`
+```
+
+Each component must be string of alphanumeric characters and underscores. No other characters are
+permitted. Every DSC Resource must define an `owner` and a `name`. Use the `group` and `area`
+components to organize DSC Resources into related namespaces. For example:
+
+- `Microsoft.SqlServer/Database`
+- `Microsoft.SqlServer.Database/Role`
+- `Microsoft.SqlServer.Database/User`
+- `Microsoft.SqlServer/Endpoint`
+- `Microsoft.SqlServer.Endpoint/Permission`
+- `Microsoft.SqlServer/Login`
+- `Microsoft.SqlServer/MaxDop`
+
+```yaml
+Type:     string
+Required: true
+Pattern:  ^\w+(\.\w+){0,2}\/\w+$
+```
+
+### version
+
+The value of this property must be the current version of the DSC Resource as a valid semantic
+version string. The version applies to the DSC Resource, not the software it manages.
+
+```yaml
+Type:     string
+Required: true
+```
+
+### get
+
+This property defines how to call the DSC Resource to get the current state of an instance.
+
+The `executable` property, defining the name of the command to call, is mandatory. The `args` and
+`input` properties are optional. For more information, see the
+[Get method's schema documentation][01].
+
+```yaml
+Type:     object
+Required: true
+```
+
+### set
+
+This property defines how to call the DSC Resource to set the desired state of an instance. It also
+defines how to process the output from the DSC Resource for this method.
+
+The `executable` property, defining the name of the command to call, is mandatory. The `args`
+`input`, `preTest`, and `returns` properties are optional. For more information, see the
+[Set method's schema documentation][02].
+
+### test
+
+This property defines how to call the DSC Resource to test whether an instance is in the desired
+state. It also defines how to process the output from the DSC Resource for this method.
+
+The `executable` property, defining the name of the command to call, is mandatory. The `args`
+`input`, and `returns` properties are optional. For more information, see the
+[Test method's schema documentation][03].
+
+### validate
+
+This property defines how to call the DSC Resource to validate an instance.
+
+The `executable` property, defining the name of the command to call, is mandatory. The `args`
+property is optional. For more information, see the [Validate method's schema documentation][04].
+
+### provider
+
+When specified, this property defines the DSC Resource as a DSC Resource Provider.
+
+For more information, see the [DSC Resource manifest provider property schema reference][05].
+
+### exitCodes
+
+This property defines a set of valid exit codes for the DSC Resource and their meaning. Define this
+property as a set of key-value pairs where:
+
+- The key is an integer that maps to a known exit code for the DSC Resource.
+- The value is a string describing the semantic meaning of that exit code for a human reader.
+
+DSC always interprets exit code `0` as a successful operation and any other exit code as an error.
+
+```yaml
+Type:     object
+Required: false
+Valid Properties:
+  Name Pattern: ^[0-9]+#
+  Value Type:   string
+```
+
+### schema
+
+This property defines how DSC should get the JSON schema to validate an instance of the DSC
+Resource. This property must always be an object that defines one of the following properties:
+
+- `command` - When you specify the `command` property, DSC calls the defined command to get the
+  JSON schema.
+- `embedded` - When you specify the `embedded` property, DSC uses the defined value as the JSON
+  schema.
+- `url` - When you specify the `url` property, DSC fetches the JSON schema from the defined URL.
+
+For more information, see the [DSC Resource manifest schema property reference][06].
+
+```yaml
+Type:     object
+Required: true
+```
+
+[01]: ./get.md
+[02]: ./set.md
+[03]: ./test.md
+[04]: ./validate.md
+[05]: ./provider.md
+[06]: ./manifest-schema.md