LDAP Refactoring to support syncronizing more than one user at a time. (#16705)

* Feature: add cron setting for the ldap settings

* Move ldap configuration read to special function

* Introduce cron setting (no docs for it yet, pending approval)

* Chore: duplicate ldap module as a service

* Feature: implement active sync

This is very early preliminary implementation of active sync.
There is only one thing that's going right for this code - it works.

Aside from that, there is no tests, error handling, docs, transactions,
it's very much duplicative and etc.

But this is the overall direction with architecture I'm going for

* Chore: introduce login service

* Chore: gradually switch to ldap service

* Chore: use new approach for auth_proxy

* Chore: use new approach along with refactoring

* Chore: use new ldap interface for auth_proxy

* Chore: improve auth_proxy and subsequently ldap

* Chore: more of the refactoring bits

* Chore: address comments from code review

* Chore: more refactoring stuff

* Chore: make linter happy

* Chore: add cron dep for grafana enterprise

* Chore: initialize config package var

* Chore: disable gosec for now

* Chore: update dependencies

* Chore: remove unused module

* Chore: address review comments

* Chore: make linter happy

vendor/github.com/robfig/cron/constantdelay.go

@@ -0,0 +1,27 @@
+package cron
+
+import "time"
+
+// ConstantDelaySchedule represents a simple recurring duty cycle, e.g. "Every 5 minutes".
+// It does not support jobs more frequent than once a second.
+type ConstantDelaySchedule struct {
+	Delay time.Duration
+}
+
+// Every returns a crontab Schedule that activates once every duration.
+// Delays of less than a second are not supported (will round up to 1 second).
+// Any fields less than a Second are truncated.
+func Every(duration time.Duration) ConstantDelaySchedule {
+	if duration < time.Second {
+		duration = time.Second
+	}
+	return ConstantDelaySchedule{
+		Delay: duration - time.Duration(duration.Nanoseconds())%time.Second,
+	}
+}
+
+// Next returns the next time this should be run.
+// This rounds so that the next activation time will be on the second.
+func (schedule ConstantDelaySchedule) Next(t time.Time) time.Time {
+	return t.Add(schedule.Delay - time.Duration(t.Nanosecond())*time.Nanosecond)
+}