[no-release-notes] go: sqle,remotesrv: Implement sql.Session lifecycle callbacks for sql.Contexts used in remotesrv RPCs.

[reltuk]

This PR changes each RPC invocation against the gRPC and HTTP servers
implementing remotesapi and cluster replication to create a sql.Context
which lives the duration of the call. The Session for that call gets
SessionCommand{Begin,End} and SessionEnd lifecycle callbacks so that it
can participate in GC safepoint rendezvous appropriately.

Previously the remotesrv.DBCache and the user/password remotesapi
authentication implementation would simply create new sql.Contexts
whenever they needed them. There could be multiple sql.Contexts for the
single server call.

[coffeegoddd]

@reltuk DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
a6b1a26	ok	5937457

version	total_tests
a6b1a26	5937457

correctness_percentage
100.0

[max-hoffman]

The handlers look good. I guess the main gap for me is whether cluster/remotesrv use of GetInterceptorSqlContext is always safe. Ex: are there any other way those servers request a context that for some reason doesn't pass through the interceptor handlers, and would error in want of the context key.

[reltuk]

The handlers look good. I guess the main gap for me is whether cluster/remotesrv use of GetInterceptorSqlContext is always safe. Ex: are there any other way those servers request a context that for some reason doesn't pass through the interceptor handlers, and would error in want of the context key.

This is a good question. This work covered inbound replication, and I think it got all the moving pieces for that part. But your question makes me think of outbound replication, in particular when/if the pushes are asynchronous, and in the context of both cluster replication and for push-on-write. I will take a pass at seeing what the state for session lifecycle stuff is there.

[coffeegoddd]

@reltuk DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
ddaa922	ok	5937457

version	total_tests
ddaa922	5937457

correctness_percentage
100.0