Store repository data in data path if not previously set

[techknowlogick]

Fixes #12292 - stores snap repo data in common directory so it isn't set to store in previous snap version path.

Previously it is set to store repo data in $HOME if not set, instead this sets it to store in AppDataPath if not set. Checked for breaking on arch & alpine and doesn't break them, however as this changes a default setting I've marked it as breaking.

[codecov-io]

Codecov Report

Merging #13991 (76c1d29) into master (c3fc190) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #13991      +/-   ##
==========================================
- Coverage   42.23%   42.21%   -0.02%     
==========================================
  Files         710      710              
  Lines       77233    77230       -3     
==========================================
- Hits        32617    32606      -11     
- Misses      39245    39250       +5     
- Partials     5371     5374       +3     

Impacted Files	Coverage Δ
modules/setting/repository.go	57.69% <100.00%> (+1.32%)	⬆️
modules/util/timer.go	42.85% <0.00%> (-42.86%)	⬇️
models/repo_mirror.go	2.38% <0.00%> (-11.91%)	⬇️
modules/cron/tasks_basic.go	87.35% <0.00%> (-3.45%)	⬇️
modules/git/utils.go	73.77% <0.00%> (-3.28%)	⬇️
modules/process/manager.go	72.50% <0.00%> (-2.50%)	⬇️
services/pull/check.go	48.90% <0.00%> (-2.19%)	⬇️
modules/log/event.go	59.90% <0.00%> (-1.89%)	⬇️
modules/git/blame.go	65.71% <0.00%> (-1.43%)	⬇️
services/mirror/mirror.go	15.78% <0.00%> (-1.11%)	⬇️
... and 10 more

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[6543]

it's nice cleanup for modules/setting/repository.go too ...

[silverwind]

Please update cheat sheet and app.example.ini (adding same comment there)

[techknowlogick]

@silverwind thanks for reminder. I have now update docs.

[silverwind]

Still missing from app.example.ini, just copy the text from the cheat sheet.

[techknowlogick]

@silverwind ah yes, I've also added in one unrelated part of docs too as it was empty and next to ROOT so it was easy enough (although I could include it in separate PR if needed)