PostGIS integration

Requires !866 (merged), !910 (merged), !913 (merged), frontend!661 (merged), architecture#14, and architecture!123
Closes #163 (closed)
⚠ Please make a base-postgis tag
✔ Before merging, please remove the WIP commit that adds base builds to this MR (for dev.arkindex.teklia.com).

TODO

• Add PostGIS to the database Dockerfile
• Add PostGIS dependencies to the backend Dockerfiles
• Polygon migration
• Zone deduplication
• Unique constraint
• Unique constraint without MD5
• ST_IsClosed constraint
• Integer coordinates constraint
• Drop arkindex.project.polygon
• Update the entire codebase
• Add unit tests
• Update js/helpers/polygon.js in the frontend
• Mitigate ST_Normalize issue
• Benchmarks
• Update dev setup docs

Possible follow-ups

• #372 — This still allows "bowtie polygons"; we could use a ST_IsRing constraint for that, but it requires extra work due to a lot of existing data not matching this constraint.
• images/consumers.py could maybe be removed; this would require some benchmarking on the ST_Scale function #413 (closed)
• Create an arkindex cleanup command to remove unused zones, unused images and unused image servers: there are over 17 million useless zones in prod and 10 million in preprod. This would be similar in code complexity to the provided deduplicate_zones command. The transcription simplification would make this command even easier #414 (closed)

Migrating

Migrate normally. If images.0005 fails and complains about duplicated polygons, run arkindex deduplicate_zones, then migrate again.