add a eglot specific jsonrpc timeout

[texaco]

Hello there. I am experiencing some problems mainly due a very slow LSP. 'rust-analyzer' in this case.

Asking for finding some references (xref-find-references) throws to me the error

jsonrpc-error: "request id=233 failed:", (jsonrpc-error-message . "Timed out")

I have been able to work this out increasing jsonrpc-default-request-timeout but I seems to me a system wide change. I think it would be nice to have a eglot custom to tween jsonrpc timeout calls.