proxy: abstract away connection pools

[awarus]

Problem

Fixes #9284

Summary of changes

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