cli: support YAML as alternative config format

[maxtorqs]

Description

Add aspire.config.yaml/.yml as alternatives to aspire.config.json. YAML is parsed via YamlDotNet's AOT-safe event-based API, converted to JSON, then deserialized through the existing source-gen pipeline. Save preserves the source format. Errors if multiple formats exist.

Things covered:

• New feature implementation (YAML reading/writing)
• AOT compatibility (event-based parser, no reflection)
• Format preservation on save
• Multiple format detection with clear error
• ConfigurationService + ConfigurationHelper YAML support
• Error strings + xlf translations auto-generated
• Unit tests
• Manual E2E test (config list, config set with YAML file)

Things to consider:

• The xlf files have state="new" for the new strings
• Schema validation: there's a JSON schema but YAML users won't get schema validation in editors, could be a follow-up
• The Exists() check is used in several places: updated it to check all formats

Not in scope (potential follow-ups):

• YAML schema for editor support
• aspire new scaffolding still creates JSON by default (correct per issue: "JSON/JSONC would remain the default")
• TOML support (mentioned in issue as a possible alternative)

Fixes #15508

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire.dev issue:
      • New issue
  • No

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 15517

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 15517"

[mitchdenny]

It doesn't make sense to introduce another configuration file format at this time since all it does is introduce ambiguity.

[adamint]

Please avoid implementation of a feature request until we can comment on that feature request.

I agree with Mitch, there is dubious benefit to this change. Closing