AAP-57817 Add Redis connection retry using redis-py 7.0+ built-in (#16176)

* AAP-57817 Add Redis connection retry using redis-py 7.0+ built-in mechanism

* Refactor Redis client helpers to use settings and eliminate code duplication

* Create awx/main/utils/redis.py and move Redis client functions to avoid circular imports

* Fix subsystem_metrics to share Redis connection pool between
  client and pipeline

* Cache Redis clients in RelayConsumer and RelayWebsocketStatsManager to avoid creating new connection pools on every call

* Add cap and base config

* Add Redis retry logic with exponential backoff to handle connection failures during long-running operations

* Add REDIS_BACKOFF_CAP and REDIS_BACKOFF_BASE settings to allow
  adjustment of retry timing in worst-case scenarios without code changes

* Simplify Redis retry tests by removing unnecessary reload logic

requirements/requirements.txt

@@ -433,7 +433,7 @@ pyzstd==0.18.0
     # via -r /awx_devel/requirements/requirements.in
 receptorctl==1.6.0
     # via -r /awx_devel/requirements/requirements.in
-redis[hiredis]==6.4.0
+redis[hiredis]==7.0.1
     # via
     #   -r /awx_devel/requirements/requirements.in
     #   channels-redis