Add config option and shortcode for Gitea version in documentation

[jolheiser]

This PR would replace #7937, which gave me this idea.

Now the Gitea version would be stored in the Hugo config, and a shortcode would print it wherever it's used.
There would only be one place to update the Gitea version for documentation.

I may have gotten a little overzealous in my swapping.
The original idea was for the installing from binary page(s), but I made a few extra changes where I thought it wouldn't hurt to mention the "latest" version in examples.

[lunny]

Will replace #7937.

[lunny]

wait until 1.9.2 releases published by CI.

[codecov-io]

Codecov Report

Merging #7940 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7940      +/-   ##
==========================================
- Coverage   41.46%   41.45%   -0.01%     
==========================================
  Files         478      478              
  Lines       63966    63966              
==========================================
- Hits        26521    26518       -3     
- Misses      33991    33993       +2     
- Partials     3454     3455       +1

Impacted Files	Coverage Δ
modules/process/manager.go	76.81% <0%> (-4.35%)	⬇️
modules/log/event.go	64.61% <0%> (-1.03%)	⬇️
models/repo_list.go	73.09% <0%> (+1.01%)	⬆️

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