Send metrics for Postgres table statistics.

[amw-zero]

What does this PR do?

Sends metrics for table statistic information stored in pg_stats. This excludes any information that includes any concrete table values, e.g. most_common_vals is excluded. That data may be sensitive and has to be treated with greater care, but the aggregate data is safe to send.

Motivation

Table statistics are very useful in determining why the query planner is choosing certain plans.

Additional Notes

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Changelog entries must be created for modifications to shipped code
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

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