[enhance:#1021]: monthly partitioning of indices

[joyant]

What problem does this PR solve?

Issue Number: #1021

Problem Summary:
This submission doesn't implement concurrent index reading due to ongoing refactoring in PR #1015.

Check List

Tests

• Unit test
• Integration test
• No code

[codecov]

Codecov Report

Attention: Patch coverage is 82.45614% with 30 lines in your changes are missing coverage. Please review.

Project coverage is 94.21%. Comparing base (f740235) to head (f56cd06).

❗ Current head f56cd06 differs from pull request most recent head cd28e60. Consider uploading reports for the commit cd28e60 to get more accurate results

Files	Patch %	Lines
index/metric_index_segment.go	82.85%	13 Missing and 11 partials ⚠️
tsdb/shard.go	62.50%	2 Missing and 1 partial ⚠️
tsdb/data_family.go	50.00%	1 Missing and 1 partial ⚠️
query/operator/tag_value_collect.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1022      +/-   ##
==========================================
- Coverage   94.38%   94.21%   -0.18%     
==========================================
  Files         400      401       +1     
  Lines       24682    24822     +140     
==========================================
+ Hits        23296    23385      +89     
- Misses       1133     1164      +31     
- Partials      253      273      +20     

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