Add cluster schedule source

[stinovlas]

Similarly to broker and backend, I added a cluster version of redis schedule source.

The implementation is in separate class. I also duplicated the tests of RedisScheduleSource and applied them to cluster source. I also added a few more tests for both RedisScheduleSource and RedisClusterScheduleSource and the taskiq_redis.schedule_source module is now completely covered.

There is no documentation for schedule sources yet, so I didn't touch it in this PR, but I'd like to find some time to add documentation about cluster mode in general and schedule sources in particular to README.

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (caeccfb) 94.24% compared to head (4074e81) 93.54%.

Files	Patch %	Lines
taskiq_redis/schedule_source.py	88.88%	3 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #50      +/-   ##
===========================================
- Coverage    94.24%   93.54%   -0.70%     
===========================================
  Files            7        7              
  Lines          191      217      +26     
===========================================
+ Hits           180      203      +23     
- Misses          11       14       +3     

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[stinovlas]

Codecov report is not updated, my second commit actually covers all lines and increases total coverage to 96%.

[stinovlas]

@s3rius Could you please take a look at this? Or perhaps delegate someone else to the review? I think this is the last piece missing to be able to fully utilize taskiq-redis in cluster mode :-).

[s3rius]

Since this source almost completely copies the default redis schedule source, I don't se any issue with merging it.

Thank you for your contribution and sorry for late reply.