Add C# management namespace and emitter output directory rules to required rules

[skywing918]

This pull request updates the validation rules in sdk-tspconfig-validation.ts to ensure that certain C# management configuration rules are now enforced as required rather than optional. This change helps enforce stricter validation for C# management TypeSpec configurations.

Validation rule updates:

• Added TspConfigCsharpMgmtNamespaceSubRule and TspConfigCsharpMgmtEmitterOutputDirSubRule to the requiredRules list, making these checks mandatory for C# management configurations.
• Removed TspConfigCsharpMgmtNamespaceSubRule and TspConfigCsharpMgmtEmitterOutputDirSubRule from the optionalRules list, reflecting their new status as required rules.

[github-actions]

Next Steps to Merge

Next steps that must be taken to merge this PR:

• ❌ The required check named TypeSpec Validation has failed. Refer to the check in the PR's 'Checks' tab for details on how to fix it and consult the aka.ms/ci-fix guide

Comment generated by summarize-checks workflow run.

[lirenhe]

Please hold the PR merge after .NET team updates all the existing tspconfig files to add the missing c# config for mgmt. plane. cc @live1206

[live1206]

please hold this until Azure/azure-sdk-for-net#60703 is done