We don't need this code in 22.2. Gets in the way slightly for tests
we're adding in the next commits that introduce probabilistic bundle
collection (further mucking with the schema of
system.statement_diagnostics_requests).

Release note: None

We enable the following ability (the first half of cockroachdb#82896):

  Pick a stmt fingerprint, declare a sampling probability which controls
  when verbose tracing is enabled for it, and a latency threshold for
  which a trace is persisted.

With a given stmt rate (say 1000/s) and a given percentile we're trying
to capture (say p99.9), we have 0.001R stmt/s in the 99.9th percentile
(1/s in our example). We should be able to set a sampling probability P
such that with high likelihood (>95%) we capture at least one trace over
the next S seconds. The sampling rate lets you control how the overhead
you’re introducing for those statements in aggregate, which if dialed up
higher lets you lower S. You might want to do such a thing for
infrequently executed statements. We do all this using the existing
statement diagnostics machinery. It looks roughly as follows

   > SELECT crdb_internal.request_statement_bundle(
      'INSERT INTO ...', -- fingerprint
      0.01,              -- sampling probability
      '120ms'::INTERVAL, -- latency target
      '15m'::INTERVAL    -- request expiration
     );

   $ cockroach statement-diag list --insecure
    No statement diagnostics bundles available.
    Outstanding activation requests:
      ID                  Statement        Sampling probability  Min latency
      770367610894417921  INSERT INTO ...  0.0100                90ms

   # wait for an eventual capture..

   $ cockroach statement-diag list --insecure
    Statement diagnostics bundles:
      ID                  Collection time          Statement
      770367073624621057  2022-06-14 00:49:33 UTC  INSERT INTO ...

   $ cockroach statement-diag download 770367073624621057 --insecure
   Bundle saved to "stmt-bundle-770367073624621057.zip"

   $ unzip stmt-bundle-770367073624621057.zip stmt
   $ cat stmt/trace.txt
    ...
        0.846ms      0.017ms      event:kv/kvserver/spanlatch/manager.go:532
                                    [n1,s1,r76/1:/Table/10{7/1-8}] waiting to
                                    acquire read latch /Table/107/1/41/7/0@0,0,
                                    held by write latch
                                    /Table/107/1/41/7/0@1655167773.362147000,0
        98.776ms     97.930ms     event:kv/kvserver/concurrency/concurrency_manager.go:301
                                    [n1,s1,r76/1:/Table/10{7/1-8}] scanning
                                    lock table for conflicting locks

We leave wiring this up to the UI and continuous capture (second half of
\cockroachdb#82896) to future PRs.

Release note: None