Add rich link preview to the login page

[juliusknorr]

Follow up of #6341 fixes #4264

cc @newhinton

[mention-bot]

@juliushaertl, thanks for your PR! By analyzing the history of the files in this pull request, we identified @ChristophWurst, @LukasReschke and @nickvergessen to be potential reviewers.

[codecov]

Codecov Report

Merging #6342 into master will decrease coverage by 16.33%.
The diff coverage is 0%.

@@              Coverage Diff              @@
##             master    #6342       +/-   ##
=============================================
- Coverage     53.31%   36.97%   -16.34%     
  Complexity    22497    22497               
=============================================
  Files          1403     1403               
  Lines         87079    87087        +8     
  Branches       1327     1327               
=============================================
- Hits          46422    32197    -14225     
- Misses        40657    54890    +14233

Impacted Files	Coverage Δ	Complexity Δ
core/Controller/LoginController.php	0% <0%> (-77.28%)	38 <0> (ø)
...mments/tests/Unit/Controller/NotificationsTest.php	0% <0%> (-100%)	4% <0%> (ø)
.../Exceptions/EncryptionHeaderKeyExistsException.php	0% <0%> (-100%)	1% <0%> (ø)
apps/files/lib/Activity/Settings/FileFavorite.php	0% <0%> (-100%)	8% <0%> (ø)
apps/files/lib/Activity/Settings/FileRestored.php	0% <0%> (-100%)	8% <0%> (ø)
lib/private/Template/ResourceNotFoundException.php	0% <0%> (-100%)	2% <0%> (ø)
...ib/private/Contacts/ContactsMenu/ActionFactory.php	0% <0%> (-100%)	2% <0%> (ø)
apps/federation/lib/Hooks.php	0% <0%> (-100%)	4% <0%> (ø)
...curity/Exceptions/StrictCookieMissingException.php	0% <0%> (-100%)	1% <0%> (ø)
...te/Authentication/Token/DefaultTokenCleanupJob.php	0% <0%> (-100%)	1% <0%> (ø)
... and 479 more

[MorrisJobke]

Broken unit tests fixed in 0326c2c