feat: Discord OAuth support

[mgkbadola]

Completes Discord OAuth integration on frontend. Can only be merged when a new version of go-pkgz/auth is released with Discord OAuth backend support (reference).

[paskal]

You can update to latest master of auth package instead and not wait for the version release.

[mgkbadola]

I've done the same, thanks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.24%. Comparing base (3646c4a) to head (d0dc113).
Report is 11 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #1824    +/-   ##
========================================
  Coverage   64.24%   64.24%            
========================================
  Files         140      140            
  Lines        3230     3230            
  Branches      773      815    +42     
========================================
  Hits         2075     2075            
+ Misses       1151     1038   -113     
- Partials        4      117   +113     

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[paskal]

@mgkbadola thanks a lot! Could you please run Remark42 with Discord auth enabled and post a screenshot of how the auth icon looks like and verify that you can log in using that method?

[badolamgk]

Hey @paskal
Here are the screenshots from my trial run.

Able to login and comment via Discord as intended.

[paskal]

@umputun interesting case: this PR broke backend tests in master (fixed in #1862), but the latest commit is merge commit which doesn't touch backend so the tests were not run. No idea what to do about it aside from asking the requestor to squash commits locally.

[mgkbadola]

Let me know how can I help to resolve this

[paskal]

No need to do anything from your side @mgkbadola, it's a fault of our CI setup which doesn't highlight the problem where it should. The failing test is already fixed.