nextcloud-notify_push: fix connecting to mysql via socket

[st3iny]

Fix #310335

Hey folks, I'm a Nextcloud developer and am currently tinkering with NixOS. Here is a little fix I came up with.

Instructing Nextcloud to connect to MySQL via a socket requires setting dbhost to localhost:/run/mysqld/mysqld.sock while Postgresql requires just the path to the socket.

Thus, the notify_push service wasn't able to connect to MySQL via a socket due to a malformed DATABASE_URL env variable. The host part is omitted if a socket is detected.

I refactored and fixed the logic when MySQL is used to always include the host part and also add the socket option to the DATABASE_URL variable. Notify_push will now connects to the MySQL socket properly.

I tested this locally with a fresh Postgres and MySQL database to make sure that there are no regressions.

# Generated strings:
DATABASE_URL='mysql://nextcloud@localhost/nextcloud?socket=/run/mysqld/mysqld.sock'
DATABASE_URL='postgresql://nextcloud/nextcloud?host=/run/postgresql'

This is my first PR here so please let me know in case something needs to be adjusted.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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