release-22.2: sql: add telemetry for statistics forecast usage

[michae2]

Backport 1/1 commits from #88539.

/cc @cockroachdb/release

---

Add a few fields to the sampled_query telemetry events that will help us
measure how useful table statistics forecasting is in practice.

Fixes: #86356

Release note (ops change): Add five new fields to the sampled_query
telemetry events:

• ScanCount: Number of scans in the query plan.
• ScanWithStatsCount: Number of scans using statistics (including
  forecasted statistics) in the query plan.
• ScanWithStatsForecastCount: Number of scans using forecasted
  statistics in the query plan.
• TotalScanRowsWithoutForecastsEstimate: Total number of rows read by
  all scans in the query, as estimated by the optimizer without using
  forecasts.
• NanosSinceStatsForecasted: The greatest quantity of nanoseconds that
  have passed since the forecast time (or until the forecast time, if it
  is in the future, in which case it will be negative) for any table
  with forecasted stats scanned by this query.

---

Release justification: low-risk change to new functionality.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[rytaft]

Reviewed 10 of 10 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @michae2)