HTTP APIs for .NET Isolated Parity

[bachuv]

This PR adds HTTP API parity (CallHttpAsync()) for .NET Isolated, but doesn't currently support Managed Identity authentication. Support for that feature will be added in the future.
 
Changes include:

• New DurableHttpRequest and DurableHttpResponse types in the Worker project
• New TaskOrchestrationContext extension method for CallHttpAsync()
• Additional changes in OutOfProcMiddleware to execute the BuiltIn::HttpActivity activity function by using the existing TaskHttpActivityShim (BuiltIn::HttpActivity is the reserved name to know when a TaskActivity should be an HTTP activity).

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation PR is ready to merge and referenced in pending_docs.md
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)
• My changes do not require any extra work to be leveraged by OutOfProc SDKs
  • Otherwise: That work is being tracked here: #issue_or_pr_in_each_sdk
• My changes do not change the version of the WebJobs.Extensions.DurableTask package
  • Otherwise: major or minor version updates are reflected in /src/Worker.Extensions.DurableTask/AssemblyInfo.cs
• My changes do not add EventIds to our EventSource logs
  • Otherwise: Ensure the EventIds are within the supported range in our existing Windows infrastructure. You may validate this with a deployed app's telemetry. You may also extend the range by completing a PR such as this one.
• My changes should be added to v3.x branch.
  • Otherwise: This change only applies to Durable Functions v2.x and will not be merged to branch v3.x.