CI: store and reuse docker builder cache for PRs

[bayandin]

Problem

If PR contains significant changes for any docker image, all builds will take a significant amount of time, as there's no intermediate cache.

Summary of changes

• Store docker builder cache for PRs and reuse it for consequent builds

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[fedordikarev]

lgtm

[github-actions]

4977 tests run: 4812 passed, 1 failed, 164 skipped (full report)

---

Failures on Postgres 17

• test_hot_standby_feedback: debug-x86-64

# Run all failed tests locally:
scripts/pytest -vv -n $(nproc) -k "test_hot_standby_feedback[debug-pg17]"

Flaky tests (2)

Postgres 17

• test_scrubber_physical_gc_timeline_deletion: release-x86-64
• test_restart_endpoint_after_switch_wal: debug-x86-64

Test coverage report is not available

_{The comment gets automatically updated with the latest test results
d92e389 at 2024-09-23T17:16:17.375Z :recycle:}

[bayandin]

For some reason, docker rebuilds everything if it has unexisting image in --cache-from.. Going to close the PR for now, maybe we can think off more clever approach in the future