Raise minimum supported PostgreSQL version to 13

[nscuro]

Description

Raises minimum supported PostgreSQL version to 13.

Also ensures that tests are executed against this minimum supported version.

Addressed Issue

Closes #1724

Additional Details

N/A

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have updated the migration changelog accordingly
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +18.46% (target: -1.00%)	✅ ∅ (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (85b3c0d)	201	132	65.67%
Head commit (a9c14a1)	7006 (+6805)	5894 (+5762)	84.13% (+18.46%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#1727)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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