Change the package base name of the Go code, from
`git.blender.org/flamenco` to `projects.blender.org/studio/flamenco`.
The old location, `git.blender.org`, has no longer been use since the
[migration to Gitea][1]. The new package names now reflect the actual
location where Flamenco is hosted.
[1]: https://code.blender.org/2023/02/new-blender-development-infrastructure/
Convert the database interface from the stdlib `database/sql` package to
the GORM object relational mapper.
GORM is also used by the Manager, and thus with this change both Worker
and Manager have a uniform way of accessing their databases.