sql: add client time to top-level execution stats

[yuzefovich]

This commit adds "client time" execution statistic to plan.txt file of the stmt bundles which tracks the amount of time that was spent waiting for the client to consume the query result (as well as constructing the PGWire messages in the first place). This should be helpful when investigating some slow queries were the bottleneck is actually the client. Note, however, this new statistic is unlikely to help in explicit EXPLAIN ANALYZE cases since in that setup we discard the output rows, so there is nothing for the client to consume.

An example output of plan.txt from the test added in this commit (where we inject 1s of sleep between reading messages corresponding to two rows):

        planning time: 104µs
        execution time: 1s
        distribution: full
        vectorized: true
        rows decoded from KV: 2 (48 B, 1 gRPC calls)
        cumulative time spent in KV: 434µs
        maximum memory usage: 10 KiB
        network usage: 0 B (0 messages)
        sql cpu time: 4µs
        client time: 1s
        isolation level: serializable
        priority: normal
        quality of service: regular

        • scan
          nodes: n1
          actual row count: 2
          KV time: 434µs
          KV contention time: 0µs
          KV rows decoded: 2
          KV bytes read: 48 B
          KV gRPC calls: 1
          estimated max memory allocated: 10 KiB
          sql cpu time: 4µs
          missing stats
          table: t@t_pkey
          spans: FULL SCAN

Fixes: #115110.

Release note (sql change): Additional execution statistic that measures "client time" is now included into plan.txt files of the stmt bundles. This client time tracks how long the query execution was blocked on the client receiving the PGWire protocol messages. Note that in EXPLAIN ANALYZE context it doesn't make much sense because in that variant the output rows are discarded and are not communicated to the client.

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[yuzefovich]

Ignore the first commit here - it's in a separate PR #118149.

[DrewKimball]

Cool!

Reviewed 1 of 1 files at r1, 8 of 8 files at r2, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @michae2)

[yuzefovich]

TFTR!

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)

[michae2]

Very nice! This is going to come in handy!

Reviewed 8 of 8 files at r2, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (and 1 stale)

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pkg/sql/explain_bundle_test.go line 650 at r3 (raw file):

	urlTemplate := getBundleDownloadURL(t, sqlutils.MatrixToStr(rows))
	prefixLength := strings.LastIndex(urlTemplate, "/")
	url := urlTemplate[:prefixLength] + "/" + strconv.Itoa(id)

Hah, wow. Very clever.