Remove custom/*.psm1 from .gitignore

[VeryEarly]

Description

for autorest based modules, custom/*.psm1 is needed to properly import custom cmdlets. Remove them from .gitignore

ls .\src\*/*.Autorest | 
    where-object {
        $name=($_.Name -split ".Autorest")[0]; 
        -not (Test-Path (Join-Path $_.FullName "custom" "Az.$name.custom.psm1"))
    }

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
  • For SDK-based development mode, 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.
  • For autorest-based development mode, include the changelog in the PR description.
  • 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]

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

[notyashhh]

Looks good!