dbmate migration running and testing tool

[samrose]

What kind of change does this PR introduce?

A tool to handle running newly created migrations, and exporting schema.sql per version of postgres.

Generated schema-.sql is used in DB test CI to check a schema dump with the file that is committed to db after running this tool. The same tool is used to run the test. The tool also runs an idempotency check after migration dump.

This tool uses https://github.com/DarthSim/overmind process manager to start/stop postgres to more cleanly manage running processes on the machine.

Also, updated docs, and slim down what is performed in test.yml, to checking idempotency and schema.sql checked in to git, as we already do the rest of the unit tests in testinfra

nix run .#dbmate-tool -- --help        
Usage: nix run .#dbmate-tool -- [options]

Options:
  -v, --version [15|16|orioledb-17|all]  Specify the PostgreSQL version to use (required defaults to --version all)
  -p, --port PORT                    Specify the port number to use (default: 5435)
  -h, --help                         Show this help message

Description:
  Runs 'dbmate up' against a locally running the version of database you specify. Or 'all' to run against all versions.
  NOTE: To create a migration, you must run 'nix develop' and then 'dbmate new <migration_name>' to create a new migration file.

Examples:
  nix run .#dbmate-tool
  nix run .#dbmate-tool -- --version 15
  nix run .#dbmate-tool -- --version 16 --port 5433

[notion-workspace]

Separate schema.sql for each image version