Fetch app updates prior to starting Nextcloud upgrade

To combat issues like https://github.com/nextcloud/server/issues/47602 we should also fetch necessary app archives around downloading the nextcloud release.

A brainstorming with @nickvergessen brought up these ideas:

• Have a step to download app archives around download the nextcloud server archive
• To do so it is necessary to query the running instance to get the enabled apps
• Allow to specify apps that shall be ignored per parameter Report, but otherwise ignore apps that are not available on appstore
• When appstore is unavailable or an app download failed report and:
  • ask whether to continue in interactive mode
  • In non-interactive mode fail,
  • continue when --force is specified.
• app folder need to be read from config.php, if something is specified then i the first writable location shall be used. Placing them there is only possible after replacing code. Easier (for now?) is to add them just to the apps directory

No files or tests are named. Start by tracing the existing Nextcloud release download flow and how the running instance exposes enabled apps. Done means app archives are fetched, unavailable apps or failures are reported, and interactive, non-interactive, and --force behavior matches the requirements.