* [MultiDB] (except ./src and ./dockers dirs): replace redis-cli with sonic-db-cli and use new DBConnector
* update comment for a potential bug
* update comment
* add TODO maker as review reqirement
* Create a SONiC configuration management service
* Perform config db migration after loading config_db.json to redis DB
* Migrate config-setup post migration hooks on image upgrade
config-setup post migration hooks help user to migrate configurations from
old image to new image. If the installed hooks are user defined they will not
be part of the newly installed image. So these hooks have to be migrated to
new image and only then they can be executing when the new image is booting.
The changes in this fix migrate config-setup post-migration hooks and ensure
that any hooks with the same filename in newly installed image are not
overwritten.
It is expected that users install new hooks as per their requirement and
not edit existing hooks. Any changes to existing hooks need to be done as
part of new image and not post bootup.
