enforce requirment for periodic config for index tables to be 24h when using boltdb shipper

[sandeepsukhani]

What this PR does / why we need it:
Boltdb shipper keeps uploading modified boltdb files by ingesters, which are by default created weekly. Queriers also downloads them during reads and keeps downloading the updated files. This means for a big cluster, files could grow a lot and ingesters have to upload bigger files even for minor updates and on the other side Queriers have to download them.

This PR enforces periodic config for index tables to be 24h when using boltdb shipper, which would help create smaller files. We anyways wanted to move towards that in future to help to add more components which can modify the index other than ingesters. The plan is to let only ingesters modify last 24 hours of the index and let other components to modify the rest of the index.

I think we should do it now while boltdb shipper is still in an experimental stage to avoid any problems in future and doing the provisioning in code for variable index file sizes.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:
Since this would not work with existing deployments which already used non-24h periodic duration, I am going to build a helper tool to rebuild boltdb files to make them have 24 hours worth of index.

Checklist

• Documentation added

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 82.14286% with 5 lines in your changes missing coverage. Please review.

Project coverage is 62.77%. Comparing base (2a596a7) to head (21ea033).

Files with missing lines	Patch %	Lines
pkg/loki/modules.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2166      +/-   ##
==========================================
- Coverage   62.91%   62.77%   -0.14%     
==========================================
  Files         162      162              
  Lines       13952    13959       +7     
==========================================
- Hits         8778     8763      -15     
- Misses       4491     4512      +21     
- Partials      683      684       +1     

Files with missing lines	Coverage Δ
pkg/loki/loki.go	0.00% <ø> (ø)
pkg/storage/store.go	66.48% <100.00%> (+4.45%)	⬆️
pkg/loki/modules.go	5.04% <0.00%> (-5.73%)	⬇️

... and 3 files with indirect coverage changes

[stale]

This issue has been automatically marked as stale because it has not had any activity in the past 30 days. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.

[slim-bean]

LGTM!