Add dependency injection support for Nexus services

[jmaeagle99]

What was changed

Add [dependency injection[(https://learn.microsoft.com/en-us/dotnet/core/extensions/dependency-injection) support for Nexus services, similar to that of activities. Public methods were named similar to the Activity-based counter parts.

Why?

Enable registration of Nexus services via dependency injection in .NET host applications.

Checklist

1. Closes [Feature Request] Support Nexus in Temporalio.Extensions.Hosting #536

2. How was this tested:

• Tests are not implemented yet

4. Any docs updates needed?

• Will check with team where appropriate documentation should be done in repo.
• Will check with team if docs.temporal.io needs to be updated.
• Proposing to add new samples to https://github.com/temporalio/samples-dotnet

[CLAassistant]

All committers have signed the CLA.

[cretz]

This whole thing looks great. I reviewed it all including the tests and I think it's solid. Only one suggestion about changing the calls to be NexusService instead of Operations.

[jmaeagle99]

Opened temporalio/samples-dotnet#118 to create a sample for these new APIs.

[cretz]

Small comment about invalid doc references (a bit sad CI didn't catch it tbh, may be an opportunity for improvement there). Feel free to merge when fixed.