Allow usage of ObjectSerializer for Cosmos bindings

[jviau]

Issue describing the changes in this PR

resolves #2911

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• 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)

Additional information

Addresses an issue with CosmosDB extension where users could not customize JSON serialization when binding directly to a POCO.

Issue:

CosmosDBConverter was not consuming any user-provided JSON serialization customization. This was a regression from #1924.

Fix:

1. Add a new option to CosmosDBExtensionOptions to provide a ObjectSerializer, defaulting to WorkerOptions.Serializer if no serializer is explicitly set.
2. Update CosmosDBConverter to use this new serializer when deserializing POCOs

Concerns / Discussion:

This is a fix for a regression introduced back in December 2023. But it COULD be seen as a new breaking behavior change for some customers. This poses some risk for this change.