Update pocketbase to version 0.23.12 and create initial superuser

[al-lac]

This PR updates pocketbase to version 0.23.12 and creates the initial superuser with a migration script.

Due to changes made to pocketbase starting with version 0.23, the intial superuser creation has to happen via the cli, the URL that is shown on the terminal or a migration script. See: pocketbase/pocketbase#5814

Tested both an upgrade and a fresh install on the Raspberry Pi 5 and Umbrel Home.

Existing users / admins will not be touched.

Closes #1969

[github-actions]

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Linting Results

Severity	File	Description
ℹ️	pocketbase/docker-compose.yml	Potentially using unsafe user in service "app": The default container user "root" can lead to security vulnerabilities. If you are using the root user, please try to specify a different user (e.g. "1000:1000") in the compose file or try to set the UID/PUID and GID/PGID environment variables to 1000.

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