[release/6.0-preview5] Fix WebApplication to read environment specific logging configuration

[halter73]

Before this change, logging configuration like the following would not be respected if it was in an environment-specific config like appsettings.Development.json (as opposed to appsettings.json).

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Debug",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  }
}

This also removes a ton of duplicate and conflicting configuration sources as noted previous closed PR: #32822

Loading less sources and not automatically reloading sources every time one is added during the "bootstrapping" of the default configuration results in far fewer file system checks leading to better startup performance.

Fixes #32383
Fixes #32432

@Pilchie

[ghost]

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[Pilchie]

Taking tell mode off of this. At this point we should email tactics for approval on why this is crucial for Preview 5.

[halter73]

@Pilchie As much as I want the logging fix, this turned into a lot. I discussed with @davidfowl and we think it's okay to wait for preview6 for this so I'll retarget to main.