[DOP-2330] - add KeyValueHwm, KeyValueIntHwm classes

[maxim-lixakov]

Change Summary

• Add KeyValueIntHWM class, designed to manage HWM for partitioned data sources like Kafka topics.
• Remove cover method from base HWM class and its use with following tests in child classes
• Add following tests and documentations for a class.

Related issue number

Checklist

• Commit message and PR title is comprehensive
• Keep the change as small as possible
• Unit and integration tests for the changes exist
• Tests pass on CI and coverage does not decrease
• Documentation reflects the changes where applicable
• docs/changelog/next_release/<pull request or issue id>.<change type>.rst file added describing change
  (see CONTRIBUTING.rst for details.)
• My PR is ready to review.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (2a7b140) 96.37% compared to head (72a5991) 96.45%.

Files	Patch %	Lines
etl_entities/hwm/key_value/key_value_hwm.py	96.96%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #71      +/-   ##
===========================================
+ Coverage    96.37%   96.45%   +0.08%     
===========================================
  Files           48       50       +2     
  Lines         1075     1128      +53     
  Branches       192      202      +10     
===========================================
+ Hits          1036     1088      +52     
  Misses          23       23              
- Partials        16       17       +1     

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