Simplify versions.sh

[yubiuser]

What does this PR aim to accomplish?:

Simplifies version.sh. Rationale: PR #4663 removed the need for sudo powers if pihole -v is called. However, this leads to issues with newer git versions (seen in #4759) as version.sh uses some git commands to get the local version and branches. Without sudo, git complains now about fatal: unsafe repository ('/var/www/html/admin' is owned by someone else).
Since PR #4875 we store local and remote version (and branch) info in /etc/pihole/versions. This PR moves the remaining functions from version.sh to updatechecker.sh. The latter is always called with sudo powers and therefore does not run into the described git issue. The remaining version.sh does nothing else than to print the requested output of /etc/pihole/versions.

Fixes: #4759

• How does this PR accomplish the above?:

1. Add a new function get_remote_version() to updatechecker.sh
2. Removes the distinction between updating the remote and local info from updatechecker. That way, we can be sure, that the local branch is updated before we get the remote hash of the the current branch. If you look at the current code, there was only one occurrence where local and remote were not called consecutively: the daily cron job. We just agreed to remove the local update from the cron job (Remove cronjob that checks local versions every 10 minutes - only check when required #4939), but this was about updating every 10 minutes. I think updating once every 24h should be fine. We already ensure that updatechecker is called at every relevant place: after a fresh install, after each pihole -up and after each checkout.
3. Move the hash functions to updatechecker.sh
4. Let pihole -v gather everything from /etc/pihole/versions

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2. I have commented my proposed changes within the code and I have tested my changes.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

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[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pihole-c-shows-version-errors/59173/13