Add HAProxy Config to reverse-proxies.en-us.md

[ghost]

Addition of HAProxy, probably need some rewriting

[6543]

Looks a bit overly complicated?

Not sure what the url rewrite magic is intended to do/fix/workaround

Also there might be an inconsistency: root path /git vs. /gitea,
why is needed at all if serving from subdomain?

[ghost]

Because it is, or at least I did not find a simpler way yet after spending my whole day trying to make it work with HAProxy.

For the url rewrite it's because Gitea wait for GET / to serve the main page, and without it it will receive GET /gitea/ instead.

The previous command work in the same way, if you ask example.com/gitea without the trailing slash you will get an empty GET, so this time HAProxy will throw you an error.

Now that I have written all that there me be a way to merge both with a better regex...
http-request replace-path /gitea\/?(.*) \/\1
seem to do the job well.

For the ROOT_PATH I misstyped it sorry, but this part is a for subdirectory, not a subdomain, so it is necessary

Edit: I see the overcomplication part, I removed the subdomain for the second example

[codecov-commenter]

Codecov Report

Merging #17407 (42a458c) into main (db89504) will increase coverage by 0.09%.
The diff coverage is 60.18%.

@@            Coverage Diff             @@
##             main   #17407      +/-   ##
==========================================
+ Coverage   45.16%   45.26%   +0.09%     
==========================================
  Files         784      788       +4     
  Lines       88229    88440     +211     
==========================================
+ Hits        39849    40028     +179     
- Misses      41908    41933      +25     
- Partials     6472     6479       +7     

Impacted Files	Coverage Δ
cmd/serv.go	2.46% <0.00%> (ø)
models/db/engine.go	31.25% <0.00%> (ø)
modules/cron/tasks_extended.go	70.16% <0.00%> (ø)
modules/csv/csv.go	73.21% <0.00%> (-2.72%)	⬇️
modules/updatechecker/update_checker.go	0.00% <0.00%> (ø)
routers/common/middleware.go	64.70% <0.00%> (ø)
routers/install/routes.go	45.76% <0.00%> (ø)
routers/web/admin/admin.go	11.34% <0.00%> (ø)
routers/web/base.go	18.00% <0.00%> (ø)
routers/web/repo/issue_content_history.go	0.00% <0.00%> (ø)
... and 42 more

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