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

scripts/backend-lint.sh

@@ -20,7 +20,7 @@ go get -u github.com/golangci/golangci-lint/cmd/golangci-lint
 
 # use gometalinter when lints are not available in golangci or
 # when gometalinter is better. Eg. goconst for gometalinter does not lint test files
-# which is not desired. 
+# which is not desired.
 exit_if_fail gometalinter --enable-gc --vendor --deadline 10m --disable-all \
   --enable=goconst\
   --enable=staticcheck