Add using_boltdb_shipper to environments/loki/main.jsonnet sample

[CandiedCode]

What this PR does / why we need it:
This resolve error for evaluating jsonnet: RUNTIME ERROR: must define boltdb_shipper_shared_store.

This also updates a failed test due to Charts Deprecation as of Nov 13, 2020. For more information, see the Helm Charts Deprecation and Archive Notice, and Update via https://github.com/helm/charts\#%EF%B8%8F-deprecation-and-archive-notice

Which issue(s) this PR fixes:
Fixes #2828

Special notes for your reviewer:

Checklist

• Documentation added
• Tests updated

[CLAassistant]

All committers have signed the CLA.

[codecov-io]

Codecov Report

Merging #2936 (8af087d) into master (78bb4bc) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2936      +/-   ##
==========================================
- Coverage   61.74%   61.73%   -0.02%     
==========================================
  Files         181      181              
  Lines       14711    14711              
==========================================
- Hits         9084     9082       -2     
- Misses       4796     4798       +2     
  Partials      831      831              

Impacted Files	Coverage Δ
pkg/querier/queryrange/downstreamer.go	95.29% <0.00%> (-2.36%)	⬇️

[kavirajk]

@sandeepsukhani should we mention about index_period here. I understand it only matters if default value differs during migration. Still wondering should we still make a note? WDYT?

[sandeepsukhani]

I think we should rewrite this example config with boltdb shipper as index store because we are defaulting to it now.
Regarding comment, I think it should be there in source jsonnet but I don't mind it being added here too.

[owen-d]

First of all, sorry for the extremely long delay in getting to this.

Regarding the implementation, I'm hesitant to include using_boltdb_shipper: false, in the installation doc. The reasoning for this is using_boltdb_shipper: true is the default and I want to avoid negating that in the installation doc.

Seeing as the confusion stems from the subsequent access of boltdb_shipper_shared_store, I think we should amend that error message instead.

How about

boltdb_shipper_shared_store: error 'must define boltdb_shipper_shared_store when using_boltdb_shipper=true. If this is not intentional, consider disabling it. boltdb_shipper_shared_store is a backend key from the storage_config, such as (gcs) or (s3)',

edit: Given how long it's been since you submitted this PR, I'll push up a new PR with my suggestion. Feel free to incorporate it yourself if you'd like the contribution credit.