sqlstats, builtins: add builtin to reset activity tables

[THardy98]

Resolves: #105843

This change introduces crdb_internal.reset_activity_tables to reset the statistics in the system.{statement|transaction}_activity tables. This is useful as an escape hatch for cases when we have stale/inaccurate statistics in the tables (i.e. if the activity job was cancelled). Users need admin to use this builtin.

Release note (sql change): Add crdb_internal.reset_activity_tables builtin to allow users to reset the statistics in the system.{statement|transaction}_activity tables. Users require admin to use this builtin.

[cockroach-teamcity]

This change is 

[maryliag]

Reviewed 5 of 6 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained

[THardy98]

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

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2. There was a merge conflict.
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You might need to create your backport manually using the backport tool.

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error setting reviewers, but backport branch blathers/backport-release-23.1-105841 is ready: POST https://api.github.com/repos/cockroachdb/cockroach/pulls/106129/requested_reviewers: 422 Reviews may only be requested from collaborators. One or more of the teams you specified is not a collaborator of the cockroachdb/cockroach repository. []

Backport to branch 23.1.x failed. See errors above.

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