[MM-27535] User invite limits for MM Cloud (#15197)

* Add a config for MM User Limit

* Adding graceful errors for if an administrator invites people passed their user limit

* Including changed vendor files

* Adding unit test

* Fix a bug

* Push up working tests (Thanks Joram)

* Add more cases, clean up logs in code

* One more case

* Refactoring based on PR comments

* Updating i18n

* Some changes based on PR review

* Remove a comment

* Bring back some translations that were somehow removed

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

vendor/modules.txt

@@ -515,7 +515,12 @@ github.com/willf/bitset
 # github.com/xtgo/uuid v0.0.0-20140804021211-a0b114877d4c
 ## explicit
 github.com/xtgo/uuid
-# go.etcd.io/bbolt v1.3.4
+# github.com/ziutek/mymysql v1.5.4
+## explicit
+# github.com/zmb3/gogetdoc v0.0.0-20190228002656-b37376c5da6a
+## explicit
+# go.etcd.io/bbolt v1.3.5
+## explicit
 go.etcd.io/bbolt
 # go.uber.org/atomic v1.6.0
 go.uber.org/atomic
@@ -612,7 +617,7 @@ golang.org/x/text/secure/bidirule
 golang.org/x/text/transform
 golang.org/x/text/unicode/bidi
 golang.org/x/text/unicode/norm
-# golang.org/x/tools v0.0.0-20200626171337-aa94e735be7f
+# golang.org/x/tools v0.0.0-20200806022845-90696ccdc692
 ## explicit
 golang.org/x/tools/go/ast/astutil
 golang.org/x/tools/go/gcexportdata
@@ -630,7 +635,8 @@ golang.org/x/tools/internal/gopathwalk
 golang.org/x/tools/internal/imports
 golang.org/x/tools/internal/packagesinternal
 golang.org/x/tools/internal/typesinternal
-# golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543
+# golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1
+## explicit
 golang.org/x/xerrors
 golang.org/x/xerrors/internal
 # google.golang.org/appengine v1.6.6