Git min requirements

[guillep2k]

Currently the home page has no mention of Gitea requiring git, or what version is needed. The code says 1.7.2 is minimum, but for what I've been reading in the issues it looks like versions prior to 1.9.0 are too problematic (I'm no git expert, though). Comments are welcomed.

[lunny]

There are also another two git version related things:

git lfs will be avaiable if enabled when git >= 2.1.2,
git commitgraph will be enabled automatically when git >= 2.18

[codecov-io]

Codecov Report

Merging #8177 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #8177   +/-   ##
=======================================
  Coverage   41.83%   41.83%           
=======================================
  Files         482      482           
  Lines       64613    64613           
=======================================
  Hits        27033    27033           
+ Misses      34110    34109    -1     
- Partials     3470     3471    +1

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

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