Support a non-SSE JSON-only mode similar to the TypeScript SDKs `enableJsonResponse: true`

[halter73]

The server needs to be configured to support JSON mode (or not). For example in the TypeScript SDK there is enableJsonResponse: true on StreamableHTTPServerTransport. At the same time, the client also has configuration for what it prefers, that's what TransportMode on SseClientTransport in the .NET SDK is for. I have no idea about Python but if the SDK is public, you can search through the source code for similarly named symbols.

Originally posted by @TomasHubelbauer in #449

[TomasHubelbauer]

Thank you for creating an issue for this 🙏

[peter-sidebotham]

Missing support/samples for streamable http with json appears to be a barrier to using MCP services with Azure networking WAF products which lack support for SSE. This includes Azure Frontdoor Service and Application Gateway (although it looks like Application Gateway may have just introduced preview support for it).