Add a Tenant property to ArmClient

[aelij]

Follow up to #44361

Please add a TenatResource Tenant { get; } property to ArmClient to simplify working with tenant-level resources (such as ARG) without having to enumerate tenants.

There's already a private _tenant field, it just needs to be exposed.

[github-actions]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @anthony-c-martin @calecarter @cemheren @j5lim @majastrz.

[jsquire]

//cc: @m-nash

[ArcturusZhang]

Hi @aelij per our design in ArmClient, it only works as if it is the current tenant - therefore whatever you want to do with tenant, you should be able to do it with ArmClient.
Could you briefly explain what you would like to do with the tenant?