Weblate database switch to PostgreSQL

Upstream only wants to support PostgreSQL and kick out MySQL support. (see https://github.com/WeblateOrg/weblate/issues/2825, https://docs.weblate.org/en/latest/admin/install.html#database-setup)

Related issues

Related to #16995 (closed)
Related to #16943
Related to #17050

Original created by @Hefee on 16994 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information