Extend the ability of gitpod regarding env variables and files

[Derroylo]

Gitpod has some basic support for env variables and files. These functions should be extended with the following functions:

• Change the config reader/writer for the new config settings
• Restore simple env variables Ability to specificy Environment Variables in a .gitpod.yml gitpod-io/gitpod#17580
• Save and restore files with multi line support. Add base64 flag to gp env gitpod-io/gitpod#10804
• Add the ability to store a whole folder as env variable extend gp-cli with possibility to save and restore folders gitpod-io/gitpod#9284
• Update the documentation

Suggested syntax for .gpt.yml:

env:
  vars:
    test: Testvalue
  files:
    auth.json: GPT_AUTH_JSON

[Derroylo]

All done, docs will be updated before the release of the next alpha version

[Derroylo]

Has been implemented in v0.5.0