Refactor docs

[jolheiser]

This PR refactors the docs and moves some things from advanced to a new developers sections, as some of them may be more appropriate for someone looking to integrate rather than an end-user.

It also removes the CI/CD and Third-party pages in lieu of an Integrations page that directs users to awesome-gitea with some examples of what they will find.

[techknowlogick]

Thanks for giving some love to the docs. Improving the docs is always appreciated. Could you also add some redirects from the deleted pages to the new location, here is the redirect file: https://github.com/go-gitea/gitea/blob/d84490a0df308f0783637e39bf5302128f9f8584/docs/static/_redirects and here are docs from netlify on the redirect format: https://docs.netlify.com/routing/redirects/#syntax-for-the-netlify-configuration-file

[codecov-io]

Codecov Report

Merging #13275 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #13275      +/-   ##
==========================================
+ Coverage   42.15%   42.17%   +0.01%     
==========================================
  Files         684      684              
  Lines       75536    75536              
==========================================
+ Hits        31843    31857      +14     
+ Misses      38468    38457      -11     
+ Partials     5225     5222       -3     

Impacted Files	Coverage Δ
modules/util/timer.go	42.85% <0.00%> (-42.86%)	⬇️
routers/repo/view.go	37.47% <0.00%> (-0.65%)	⬇️
modules/git/repo.go	46.70% <0.00%> (+0.50%)	⬆️
services/pull/patch.go	55.68% <0.00%> (+1.70%)	⬆️
services/pull/temp_repo.go	29.78% <0.00%> (+3.19%)	⬆️
modules/git/utils.go	77.04% <0.00%> (+3.27%)	⬆️
services/pull/check.go	52.55% <0.00%> (+3.64%)	⬆️
modules/charset/charset.go	73.03% <0.00%> (+4.49%)	⬆️
modules/indexer/stats/db.go	60.86% <0.00%> (+8.69%)	⬆️

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[jolheiser]

@techknowlogick I think I got it right? I'm not sure if I can test it locally, but afaik that should be correct. Not sure if there's a better way with the en-us part, but I don't think I changed the other languages (other than api-usage because it was just a dir change).

[techknowlogick]

technically you can test locally (using the netlify cli tool), but this LGTM and will test once merged (If we were using Github integration w/ netlify then it have a URL for each URL, but Drone works better for our workflow and will allow us to switch to gitea.com with less issues)

[techknowlogick]

🚀