Refactor HTTP transport

[sdesaiLULA]

This pull request refactors the HTTP transport layer to improve extensibility and consistency, mainly by introducing the IWolverineHttpTransportClient interface, consolidating content type constants, and supporting both batch and inline sending modes. It also updates tests and documentation to reflect these changes.

Transport Client Improvements

• Introduced the IWolverineHttpTransportClient interface for sending messages, allowing custom implementations and improving dependency injection flexibility. The default WolverineHttpTransportClient now implements this interface. [1] [2]
• Updated service registration to use the interface, enabling easy substitution for custom behavior.

Content Type Consistency

• Moved envelope content type constants (EnvelopeContentType, EnvelopeBatchContentType) to HttpTransport, ensuring a single source of truth and updated all usages accordingly. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Endpoint and Sender Enhancements

• Added support for inline sending mode via the new InlineHttpSender class, and updated HttpEndpoint to select the appropriate sender based on mode. [1] [2]
• Changed mode support logic in HttpEndpoint to allow all endpoint modes, including inline and buffered.
• Exposed SupportsNativeScheduledSend on HttpEndpoint and enabled configuration via the publishing extension method. [1] Fb95d5f0L13R13, [2]

Documentation and Sample Updates

• Improved comments in sample configuration to clarify batch vs. inline publishing and how to enable native scheduled sends. [1] [2]

Testing Updates

• Added comprehensive unit tests for HttpEndpoint covering sender creation, listener building, and mode support.
• Updated existing tests to use the new content type constants and interface-based client. [1] [2] [3] [4] [5]

[jeremydmiller]

@sdesaiLULA Good stuff, thank you!