Add 'make prepare-tools' for offline builds

[typeless]

Add a new make target make prepare-tools that install all the needed tools for us.
Not sure if this is actually better or helpful at all for use cases like #7997.

[typeless]

It seems that the OpenSUSE build service gets the build prerequisites for a package by a declarative description/configuration. So, this PR probably does not help at all. The users of UBS can handle this on their side without help from Gitea.

[codecov-io]

Codecov Report

Merging #8011 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #8011      +/-   ##
==========================================
- Coverage    41.6%   41.59%   -0.01%     
==========================================
  Files         479      479              
  Lines       64106    64106              
==========================================
- Hits        26670    26667       -3     
- Misses      33980    33981       +1     
- Partials     3456     3458       +2

Impacted Files	Coverage Δ
modules/process/manager.go	76.81% <0%> (-4.35%)	⬇️
models/repo_list.go	73.17% <0%> (-0.98%)	⬇️
models/unit.go	67.56% <0%> (+5.4%)	⬆️

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[sapk]

Maybe we can keep those checks but call make prepare-tools if needed ?

[typeless]

Do you mean check the tools at the call sites or check them under prepare-tools?

[typeless]

Decide what we can help in the future when people complain about it. 😉