[Task]: 1.0: Support multi-tenancy

https://github.com/a2aproject/A2A/pull/1195 updates core proto with extra HTTP bindings prefixed with `/{tenant}`. It should be supported.

It's not fully clear how to represent it for JSON-RPC, also HTTP+JSON/REST protocol binding in the spec doesn't mention it, see https://github.com/a2aproject/A2A/issues/1273 and https://a2a-protocol.org/latest/specification/#53-method-mapping-reference.