Add group to tools #268

Hello, I would like to add a group request endpoint, and mark which group it belongs to when registering tools. When using the SSE endpoint, describe the group in the path or parameters. When the client pulls the tool list, it returns the tools of the specified group (if no group is specified, all are returned).

I expect to solve the problem:

1 When a server has many tools, I don't want to use multiple endpoints to group these tools, which is simpler when used in a framework like Spring.
2 Configure different groups to express different agents by obtaining different tool lists.

Note: Alternatively, add a group by interface to handle the group names passed by the SSE endpoint. This interface receives the group name and tools list context, and returns the tools list corresponding to the group name.