[TypeSpec to SDK] .NET specific gaps

[josefree]

• Tests for features moving to stable/GA are required for .NET SDK releases, but the gating is unclear, making it easy for service teams to bypass this requirement.
• APIView is already covered during SDK PR review, so it should either be removed from the release pipeline requirements or be automatically approved.
• SDK PRs should be approved by the SDK engineer on duty, or auto-approved if all checks pass, rather than being approved by the service team.

[josefree]

@ArthurMa1978 raised these requirements for .NET