[Eng] Improve typespec devexp with `Update-DevTSPModule`

[VeryEarly]

Description

instruction: https://github.com/VeryEarly/azure-powershell/blob/yabo/tsp-client/tools/AzDev/src/Typespec/README.md

• will remove legacy doc before merging
• will update changelog before merging
• will update autorest.powershell to not delete tspconfig.yaml

Mandatory Checklist

• Please choose the target release of Azure PowerShell. (⚠️Target release is a different concept from API readiness. Please click below links for details.)

  • [ ] General release
  • [ ] Public preview
  • [ ] Private preview
  • [ ] Engineering build
  • [ ] No need for a release

• [ ] Check this box to confirm: I have read the Submitting Changes section of CONTRIBUTING.md and reviewed the following information:

• SHOULD update ChangeLog.md file(s) appropriately
  • Update src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md.
    • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header in the past tense.
  • Should not change ChangeLog.md if no new release is required, such as fixing test case only.
• SHOULD regenerate markdown help files if there is cmdlet API change. Instruction
• SHOULD have proper test coverage for changes in pull request.
• SHOULD NOT adjust version of module manually in pull request

[azure-client-tools-bot-prd[bot]]

Thanks for your contribution! The pull request validation has started. Please revisit this comment for updated status.

[isra-fel]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 3 pipeline(s).

[VeryEarly]

Do we want to name TSP modules ***.TSP like ***.AutoRest? Could reduce a bit confusion but needs to update lots of scripts

Yes, update scripts/pipelines could be a heavy work, we shall plan it separately.