chore(dbtest): Update boundary default test postgres image

[RyanDerr]

Overview

Boundary currently only supports version 15+ of postgres, this PR updates the default postgres testing image version to the most updated postgres image tag.

Changes To Test & Queries To Support PG V17

• Updates to count queries to clamp negative values to zero since PostgreSQL documents that reltuples can be -1 when stats are unknown from the planner.
• Updated some of the migration tests that were relying on implicit row ordering from postgres, to be deterministic since PSQL does not guarantee row order without an ORDER BY
  • Note that UNIONS also do not guarantee any order.
• Updates to the grant comparison helper was also made to be order insensitive so it validates the actual grant content rather than comparing both order and content of what's returned.

Notes

• A future PR likely should publish a new image to hashicorpboundary/postgres for 18-alpine and update the default image tag to 18-alpine in the testing/dbtest/docker/Makefile to boundary is tested locally against the latest supported version of pg.

PCI review checklist

• I have documented a clear reason for, and description of, the change I am making.
• If applicable, I've documented a plan to revert these changes if they require more than reverting the pull request.
• If applicable, I've documented the impact of any changes to security controls.
  Examples of changes to security controls include using new access control methods, adding or removing logging pipelines, etc.