Limit sync2

[jvillafanez]

Description

Include a sync limiter and disable LDAP users automatically if the number of users is above the limit
Cherry-picked and updated from #35105

Related Issue

https://github.com/owncloud/enterprise/issues/3245

Motivation and Context

How Has This Been Tested?

Requires testing with the latest ownCloud

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Database schema changes (next release will require increase of minor version instead of patch)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests only (no source changes)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation ticket raised:
• Changelog item, see TEMPLATE

TODO:

• Update "since" tag
• Check migrations (might need to change the filename)

[codecov]

Codecov Report

Merging #36563 into master will decrease coverage by 0.11%.
The diff coverage is 47.49%.

@@             Coverage Diff              @@
##             master   #36563      +/-   ##
============================================
- Coverage     64.68%   64.57%   -0.12%     
+ Complexity    19118    19112       -6     
============================================
  Files          1269     1275       +6     
  Lines         74775    74858      +83     
  Branches       1320     1317       -3     
============================================
- Hits          48369    48340      -29     
- Misses        26018    26131     +113     
+ Partials        388      387       -1

Flag	Coverage Δ	Complexity Δ
#javascript	53.88% <13.04%> (-0.24%)	0 <0> (ø)
#phpunit	65.75% <49.71%> (-0.11%)	19112 <62> (-6)

Impacted Files	Coverage Δ	Complexity Δ
lib/private/User/Account.php	76% <ø> (ø)	10 <0> (ø)	⬇️
core/routes.php	48.71% <ø> (ø)	0 <0> (ø)	⬇️
core/templates/sync/htmlmail.hardlimit.php	0% <0%> (ø)	0 <0> (?)
core/templates/sync/htmlmail.softlimit.php	0% <0%> (ø)	0 <0> (?)
core/register_command.php	0% <0%> (ø)	0 <0> (ø)	⬇️
core/Migrations/Version20191211175735.php	0% <0%> (ø)	5 <5> (?)
core/Migrations/Version20170221114437.php	0% <0%> (ø)	2 <1> (+1)	⬆️
lib/private/Server.php	85.14% <100%> (+0.07%)	128 <0> (ø)	⬇️
lib/private/User/SyncLimiter.php	100% <100%> (ø)	8 <8> (?)
core/js/js.js	55.05% <100%> (ø)	0 <0> (ø)	⬇️
... and 49 more

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[jvillafanez]

I don't think I can rise coverage easily.
AccountMapper changes would require to modify the DB data, but restoring the previous state won't be clean taking into account how the tests are planned at the moment.
SyncBackend requires mocking 2-level dependencies (or more) due to the SyncService being created and not injected. In addition, the code is quite complex around the notifications, so we should consider to move that piece out to a different class.

[jvillafanez]

❗ /settings/users/<uid>/enabled endpoint allows enabling the users over the limit. This is a bug that should be fixed. The limit will be restored in the next login / sync, but it's very likely that a different user is disabled to force the limit.