updated docs with caveat for authorized_keys

[divbhasin]

Context

Gitea makes authorized_keys backups by default. People following along with the "Installing with Docker" > "SSH Container Passthrough" section are asked to symlink their authorized_keys folder with a volume that is mounted inside the container, as described here: https://docs.gitea.io/en-us/install-with-docker/#ssh-container-passthrough. However, this symlink can end up pointing to a backup, leading to ssh not working as described in #12625.

Solution

Add the recommendation given by the author of #12625 as a second option to the docs and tell users to turn off authorized_keys backup if they want to go with the first option.

[codecov-commenter]

Codecov Report

Merging #13030 into master will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #13030      +/-   ##
==========================================
- Coverage   42.55%   42.54%   -0.01%     
==========================================
  Files         672      672              
  Lines       73715    73715              
==========================================
- Hits        31370    31364       -6     
  Misses      37269    37269              
- Partials     5076     5082       +6     

Impacted Files	Coverage Δ
modules/notification/ui/ui.go	80.55% <0.00%> (-2.78%)	⬇️
models/unit.go	46.57% <0.00%> (-2.74%)	⬇️
services/pull/check.go	47.69% <0.00%> (-2.31%)	⬇️
models/notification.go	65.76% <0.00%> (-0.91%)	⬇️
models/error.go	34.34% <0.00%> (-0.85%)	⬇️
routers/repo/view.go	37.47% <0.00%> (-0.65%)	⬇️
modules/notification/mail/mail.go	34.48% <0.00%> (ø)
services/mailer/mail.go	55.91% <0.00%> (+1.07%)	⬆️
modules/log/event.go	59.43% <0.00%> (+1.88%)	⬆️
modules/indexer/stats/db.go	52.17% <0.00%> (+8.69%)	⬆️
... and 2 more

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