sql: use go runtime task groups to measure CPU/RAM usage per session

[knz]

This uses the experimental task group API (see related RFC)
to measure CPU/RAM usage separately per SQL session.

The experimental task group API is available in this custom
branch of the Go runtime:
cockroachdb/go@crdb-fixes (commits)

The interface for the API in the new library go-plus
(github.com/cockroachdb/go-plus) ensures that the code runs without
error even when the custom go runtime is not being used.

Note that this implementation does not yet collect CPU/RAM usage on other
nodes when a session runs distributed queries.

[cockroach-teamcity]

This change is 

[knz]

cc @cockroachdb/sql-observability @cockroachdb/obs-inf-prs can one of you folk help? I'm modifying the session proto to add some field and getting some build errors:

src/sessions/sessionsPage.fixture.ts(47,5): error TS2322: Type '{ node_id: number; username: string; client_address: string; application_name: string; start: { seconds: Long.Long; nanos: number; }; last_active_query: string; id: Uint8Array; ... 7 more ...; toJSON: () => {}; }' is not a
ssignable to type 'Session'.
  Object literal may only specify known properties, and 'cpu_time' does not exist in type 'Session'.
src/sessions/sessionsPage.fixture.ts(55,3): error TS2739: Type '{ node_id: number; username: string; client_address: string; application_name: string; alloc_bytes: Long; max_alloc_bytes: Long; start: { seconds: Long; nanos: number; }; last_active_query: string; ... 4 more ...; toJSON:
() => {}; }' is missing the following properties from type 'Session': sched_ticks, nanos, large_bytes
src/sessions/sessionsPage.fixture.ts(119,5): error TS2322: Type '{ node_id: number; username: string; client_address: string; application_name: string; active_queries: { id: string; sql: string; start: { seconds: Long.Long; nanos: number; }; phase: cockroach.server.serverpb.ActiveQuery
.Phase.EXECUTING; txn_id: Uint8Array; sql_anon: string; }[]; ... 10 more ...; toJSON: () => {}; }' is not assignable to type 'Session'.
  Object literal may only specify known properties, and 'cpu_time' does not exist in type 'Session'.
error Command failed with exit code 2.

This somewhere in cluster-ui. What am I missing? Why does this not automatically update when I modify the .proto file?

[knz]

oh nevermind, I should learn how to read the error message. I was able to fix it. Thanks