Fix broken docs/en links

[ndresx]

Summary
I have tried to edit an existing page in the documentation and landed on GitHub's 404 page because the edit link was missing the language code. This PR is adding those to problematic links.

I have not touched any references in older blog posts or changelogs, but can also do this if you want.

As a side note it might be good to add canonical/hreflang tags to improve search engine indexing. At least a redirect from non-en to en might be helpful since these pages are now already indexed and users who come from there will still land on these pages (the sidebar isn't fully rendered there for some reason).

Test plan
N/A

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[codecov-io]

Codecov Report

Merging #3507 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3507   +/-   ##
=======================================
  Coverage   62.28%   62.28%           
=======================================
  Files         181      181           
  Lines        6700     6700           
  Branches        5        5           
=======================================
  Hits         4173     4173           
  Misses       2525     2525           
  Partials        2        2

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