Deprecate old docs and add references to the new docs

[tzolov]

For backward compatibility update the old https://github.com/modelcontextprotocol/modelcontextprotocol/tree/main/docs/sdk/java docs content to reference the new docs.

Then after while we can remove it al together.

[tzolov]

Here is the PR to track: modelcontextprotocol/modelcontextprotocol#2259