Automated install script and maintenance

[Root-Core]

---

• I have read the contributing guideline and understand that I have made the correct modifications

---

Description:

This implements an automated method to install nextcloud via env variables.

This implements some automated maintenance steps, which fixes annoying warnings in the admin panel and is more comfortable.

This implements a automated way to reset the admin's password via env variables.

This implements a loading mechanism for env variables from a file.

Disclaimer: I took some inspiration / code from the mariadb container.

Benefits of this PR and context:

Improved UX and automated deployment.

How Has This Been Tested?

This was tested with docker compose and mariadb. I tested multiple instances.

It doesn't affect other parts of the code, but the order of modifying files is altered to prevent issues.

Source / References:

https://github.com/linuxserver/docker-mariadb/blob/912096e6bcc4b8a0b0ec6b20f347a4e93dad7d1e/root/etc/s6-overlay/s6-rc.d/init-mariadb-initdb/run#L23

https://github.com/linuxserver/docker-mariadb/blob/912096e6bcc4b8a0b0ec6b20f347a4e93dad7d1e/readme-vars.yml#L43

[github-actions]

Thanks for opening this pull request! Be sure to follow the pull request template!

[Root-Core]

I found an issue with the current script: it does not create the CAN_INSTALL file.
I don't know why it works at all in the current container script. However, the script creates the file now.

[LinuxServer-CI]

I am a bot, here are the test results for this PR:
https://ci-tests.linuxserver.io/lspipepr/nextcloud/31.0.9-pkg-1496f682-dev-8c2c2321c0245252d31a9c07d7db766309c6c783-pr-523/index.html
https://ci-tests.linuxserver.io/lspipepr/nextcloud/31.0.9-pkg-1496f682-dev-8c2c2321c0245252d31a9c07d7db766309c6c783-pr-523/shellcheck-result.xml

Tag	Passed
amd64-31.0.9-pkg-1496f682-dev-8c2c2321c0245252d31a9c07d7db766309c6c783-pr-523	✅
arm64v8-31.0.9-pkg-1496f682-dev-8c2c2321c0245252d31a9c07d7db766309c6c783-pr-523	✅