Migrate Dapr.Configuration into separate client

[WhitWaldo]

Implementation for work described in #1427

With 1.16, we'll create a new client and run both the version in Dapr.Client and the separate package in parallel. Mark the affected methods in Dapr.Client with an [Obsolete("Use the Dapr.Configuration NuGet package instead as this method will be removed from Dapr.Client in v1.17")].

Do note that once I merge this PR, we'll be replacing the use of the [Obsolete] attribute with [Experimental] going forward.

[WhitWaldo]

@siri-varma Assuming you're still free to take on this work, could you please use an "/assign" here for tracking?

[WhitWaldo]

@siri-varma Please note that I changed how each of the external client packages are expected to handle extension method DI registration in this PR. Make sure you're synced on branch "release-1.16" and make sure your DI extension method follows the example here.