* LDAP: Allow an user to be synchronised against LDAP
This PR introduces the /ldap/sync/:id endpoint. It allows a user to be synchronized against LDAP on demand.

A few things to note are:

LDAP needs to be enabled for the sync to work
It only works against users that originally authenticated against LDAP
If the user is the Grafana admin and it needs to be disabled - it will not sync the information
Includes a tiny refactor that favours the JSONEq assertion helper instead of manually parsing JSON strings.