[stable12] add option to use legacy v2 auth with s3

[MorrisJobke]

Backport of #7570

[mention-bot]

@MorrisJobke, thanks for your PR! By analyzing the history of the files in this pull request, we identified @Xenopathic to be a potential reviewer.

[MorrisJobke]

I just tested it and it still works 👍

[codecov]

Codecov Report

Merging #7758 into stable12 will increase coverage by 1.97%.
The diff coverage is 6.54%.

@@ Coverage Diff @@## stable12 #7758 +/- ##
==============================================
+ Coverage 53.9% 55.88% +1.97% + Complexity 22724 21222 -1502 
==============================================
Files 1384 1290 -94 Lines 87036 81126 -5910 Branches 1331 1331 ==============================================
- Hits 46920 45337 -1583 + Misses 40116 35789 -4327

Impacted Files	Coverage Δ	Complexity Δ
lib/private/Files/ObjectStore/S3Signature.php	0% <0%> (ø)	28 <28> (?)
...ib/private/Files/ObjectStore/S3ConnectionTrait.php	68.08% <77.77%> (+10.3%)	28 <3> (+5)	⬆️
lib/private/Memcache/Memcached.php	0% <0%> (-57.9%)	31% <0%> (ø)
lib/private/Files/Storage/DAV.php	7.29% <0%> (-57.53%)	161% <0%> (ø)
lib/private/Files/Cache/Propagator.php	94.93% <0%> (-1.27%)	16% <0%> (ø)
lib/private/Repair/Collation.php	0% <0%> (ø)	16% <0%> (ø)	⬇️
apps/dav/lib/CalDAV/Activity/Provider/Calendar.php	0% <0%> (ø)	43% <0%> (ø)	⬇️
apps/files_external/lib/AppInfo/Application.php
...xternal/lib/Lib/Auth/Password/LoginCredentials.php
apps/files_external/lib/Command/Export.php
... and 136 more