server side "disconnect client" functions

we need a way to disconnect clients from the server side. ideally both through, ctx.disconnect_identity(identity: Identity) and ctx.disconnect_connection_id(connection_id: ConnectionId).
this is required to be able to build ban systems as custom clients can just not react to any "server says disconnect" setups.
a timeout system also requires this but can be worked around with the "server says disconnect" setups but it isn't nice and can be ignored on the client side as mentioned.
the disconnect_connection_id alternative is needed when multiple clients can connect to the same identity at the same time and we don't want to disconnect all connections or something like that. (it's mostly to have the option)
doing a direct ctx.disconnect_sender() is not as useful as it doesn't work with scheduled reducers/procedures.

Requested by @xDovos via the SpacetimeDB site.

The issue names no files, tests, or entry points. Start by tracing the server-side connection lifecycle and the existing "server says disconnect" path, then determine how scheduled reducers and procedures access connection context. Done means exposing identity-wide and individual connection-ID disconnect operations, including the multiple-connections case, with coverage for both behaviors.