CLI command for list of enabled metrics

At the moment a user can't receive the list of enabled metrics anywhere, just the list of enabled metrics' sources. So, we need to:

• Move current logic from

 ignite metric list
 ignite metric enable
 ignite metric disable

to 

ignite metric source list
ignite metric source enable
ignite metric source disable

• Change

 ignite metric list

to return the actual list of enabled metrics