Update exporter extension DI sample

[omribz156]

Fixes #4128.

Updates the MyExporterExtensions sample so it demonstrates the dependency-injection-aware registration pattern described in the same guide.

Changes:

• adds named options support to AddMyExporter
• configures exporter options through TracerProviderBuilder.ConfigureServices
• creates the processor through the AddProcessor(serviceProvider => ...) factory overload
• references OpenTelemetry.Api.ProviderBuilderExtensions from the sample project so the DI builder extensions are available

Verification:

• git diff --check
• dotnet --version could not run because this checkout requires SDK 10.0.300 via global.json, and no compatible .NET SDK is installed locally.

This was implemented with Codex assistance, with the final diff reviewed manually and kept to the exporter registration docs sample.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: omribz156 / name: Omri SirComp (769b6dd, a395687)

[martincostello]

The human behind this PR needs to sign the CLA.

[rajkumar-rangaraj]

Should we consider adding an overload method, so anyone who needs a simpler option can use the current implementation?

[omribz156]

Thanks, yes — I added a follow-up commit that keeps the simple AddMyExporter() overload on the original direct processor path, and makes the DI/options path explicit through overloads that take Action<MyExporterOptions> (optionally with a name).

Verification: git diff --check passes. Full dotnet verification is still blocked locally because this checkout pins SDK 10.0.300 in global.json, and no compatible SDK is installed here.

This follow-up was Codex-assisted, with the final diff reviewed before pushing.