Implement SDL CLI 'healthcheck' -command

Implement SDL CLI 'healthcheck' -command

Implement a new 'healthcheck' -command for SDL CLI to validate
healthiness of the SDL database. Under the hood 'healthcheck' -command
calls Redis client's 'Master' and 'Slaves' APIs and parses from the
responses master and slave Redis servers related fields to show the
overall healthiness of the SDL database backend.

Redis client's version was upgraded from v6.15.9 to v7 v7.4.1,
because old client didn't support 'Master' and 'Slaves' Redis
sentinel APIs. Also implement usage of Redis client's
'NewSentinelClient' client connection to read state information via
'Master' and 'Slaves' APIs. In case of standalone Redis server
deployment state information is read via Redis client's 'Info' API.

Issue-Id: RIC-113

Signed-off-by: Timo Tietavainen <timo.tietavainen@nokia.com>
Change-Id: I7d964ac5c3d10cc90075977e2b11da7a9c11949d