Extract relation metrics for toast tables

[bonnefoa]

What does this PR do?

We currently only pull relation metrics from pg_stat_user_tables and pg_stat_user_indexes. However, those tables don't include toast tables so we're missing metrics on toast tables.

Motivation

Since data bigger than 2KB will be split in chunk of 2KB and moved in the toast table, an update of a table with toast data can generate hundred of tuple updates behind the hood that will not appear on the user table's stats.
We need to fetch them explicitly to get relations metrics like number of live rows/dead rows in the toast table and number of returned rows.

Additional Notes

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached
• If the PR doesn't need to be tested during QA, please add a qa/skip-qa label.

[codecov]

Codecov Report

Merging #14156 (abf1991) into master (4b4ff18) will increase coverage by 0.01%.
Report is 1743 commits behind head on master.
The diff coverage is 100.00%.

Additional details and impacted files

Flag	Coverage Δ
postgres	92.05% <100.00%> (+0.38%)	⬆️

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[FlorentClarret]

Hey @bonnefoa 👋 Just a heads up that we will freeze the repo on Friday for Agent 7.47. Let us know if you want to include this in the next release!

[bonnefoa]

I need to rework this PR, it won't be ready for the next freeze. Thanks for the headsup :)

[FlorentClarret]

Hey @bonnefoa, very friendly reminder this PR is still pending. Let us know if you need a hand

[FlorentClarret]

Closing this PR since it's still a draft, feel free to re-open it if needed 🙂