Allow configurability of index refreshes

[rcoy-v]

Changes

• Handle Elasticsearch index refreshes with client based on Grafeas configuration value.
• Remove registration of default Grafeas storage providers.

The current way of creating the ES storage conflicts with how Grafeas gives access to config file. I have not landed on a completely good solution to refactor things one way or another. For now, only read refresh the Grafeas way, and leave existing code. This will be refactored to a more cohesive approach once the ES host is read from config as well.

[codecov[bot]]

Codecov Report

Merging #24 (6a30798) into main (4b4d320) will increase coverage by 0.79%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #24      +/-   ##
==========================================
+ Coverage   88.40%   89.20%   +0.79%     
==========================================
  Files           2        3       +1     
  Lines         483      500      +17     
==========================================
+ Hits          427      446      +19     
+ Misses         34       33       -1     
+ Partials       22       21       -1     

Impacted Files	Coverage Δ
go/config/config.go	100.00% <100.00%> (ø)
go/v1beta1/storage/elasticsearch.go	87.06% <100.00%> (+0.84%)	:arrow_up:

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