[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[bot]]

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).

:exclamation: 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 :warning:
tsdb/shard.go	62.50%	2 Missing and 1 partial :warning:
tsdb/data_family.go	50.00%	1 Missing and 1 partial :warning:
query/operator/tag_value_collect.go	0.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ 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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