* feat: implement CONFIG GET command
The command returns all the matched arguments and their current values.
In addition, this PR adds mutability semantics to each config - whether it can be
changed at runtime.
Fixes#1700
Signed-off-by: Roman Gershman <roman@dragonflydb.io>
---------
Signed-off-by: Roman Gershman <roman@dragonflydb.io>