fix(redis): import redis pipeline using full path

[olksdr]

Currently Sentry uses redis-py-cluster==2.1.0 which does not expose the ClusterPipeline as a top level object. The fix was introduced in version 2.1.1 and another fix in 2.1.2 see https://github.com/Grokzen/redis-py-cluster/blob/master/docs/release-notes.rst

And getting following error

09:05:04 [INFO] sentry.plugins.github: apps-not-configured
Traceback (most recent call last):
  File "/Users/olksdr/dev/sentry/.venv/lib/python3.8/site-packages/sentry_sdk/integrations/redis.py", line 123, in setup_once
    _patch_rediscluster()
  File "/Users/olksdr/dev/sentry/.venv/lib/python3.8/site-packages/sentry_sdk/integrations/redis.py", line 88, in _patch_rediscluster
    pipeline_cls = rediscluster.ClusterPipeline
AttributeError: module 'rediscluster' has no attribute 'ClusterPipeline'

This PR makes sure to use the full path to import rediscluster.pipeline.ClusterPipeline which always available in any version now.

See errors in integration tests on getsentry/relay#1413 and getsentry/relay#1414 where the sentry master branch is used to run those tests with newly updated python sentry-sdk dependency.

Related changes which "broke" the sdk for redis-py-cluster==2.1.0 were introduced in #1543

[jjbayer]

@olksdr Thanks for this!

Let's wait for SDK owners' approval before merging.

[sl0thentr0py]

thx @olksdr I'm adding a test matrix entry from #1562 that captures this.