Support CIMD for Remote OAuth MCP Servers

[ellismg]

In 0.0.389 we added support for Remote MCP Servers protected by OAuth that support the DCR (Dynamic Client Registration) standard. DCR allows an OAuth client to register itself with an OAuth server "just in time" instead of requiring the client to have been pre-registered with the server (with a fixed client ID).

There are some downsides to DCR for server operators, and so MCP has also adopted CIMD as a standard that fixes some of these issues. In CIMD the client uses a URL as a client ID and that URL points at a JSON document that the server can use to discover information about the client.

We should support CIMD in copliot, VS Code supports this today, and we'd like to be at parity here.