sql: SHOW/CANCEL QUERIES/SESSIONS needs work for multi-tenancy

[tbg]

See here for background

SHOW/CANCEL (and some others) uses the statusServer which is not available on a SQL tenant server. However, in phase 2, there's only ever at most one SQL tenant process running on behalf of a given tenant, meaning that all sessions and queries are available via the local node.

When running in a tenant process, the necessary information should thus be available (but is not, since the status server is not supplied). This can be fixed in a number of ways, the most desirable seemingly being to thin out the dependency on the status server interface to reflect only what's required of it, and injecting a "local-only" impl when starting up as a tenant server.

Similarly, when actually cancelling requests, this should call into the local process (since all queries/session are local).

Tenatively labeling this a blocker since there are many places that use the status server and this solution can fix all of them. The cumulative fallout of having none of them work may qualify as a blocker.