Create Roslyn analyzer to obsolete use of `TelemetryClient`?

We should obsolete `TelemetryClient` use, since we want to remove it in the next major release in favor of OpenTelemetry and `System.Diagnostics`. Since this is just a DI registered service, we could create an analyzer to emit warning diagnostics with guidance on how to use OpenTelemetry instead.

We could also use this analyzer for other things in the future

No files, tests, or entry points are named in the issue; begin by locating the C# project and its dependency-injection registration for TelemetryClient. Define the analyzer scope and warning guidance for replacing TelemetryClient with OpenTelemetry and System.Diagnostics, with completion marked by diagnostics that cover the agreed usages and guidance for migration.

Written by the indexing model from the issue text.