autosharding: add config parsing functionality

[easwars]

RELEASE NOTES: none

[codecov]

Codecov Report

❌ Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.15%. Comparing base (30ce1d5) to head (46e4340).

Files with missing lines	Patch %	Lines
balancer/autosharding/autosharding.go	88.23%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9323      +/-   ##
==========================================
+ Coverage   83.06%   83.15%   +0.08%     
==========================================
  Files         423      424       +1     
  Lines       35236    35253      +17     
==========================================
+ Hits        29270    29313      +43     
+ Misses       4449     4436      -13     
+ Partials     1517     1504      -13     

Files with missing lines	Coverage Δ
balancer/autosharding/autosharding.go	88.23% <88.23%> (ø)

... and 26 files with indirect coverage changes

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