blockstore/blockservice: change option to WriteThrough(enabled bool)

[hsanjuan]

This allows passing in a boolean to indicate if we want to use the option or not, which provides better ergonomics for initialization.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 60.41%. Comparing base (7c459af) to head (f9bac13).

Files with missing lines	Patch %	Lines
blockstore/blockstore.go	0.00%	2 Missing ⚠️

@@           Coverage Diff           @@
##             main     #749   +/-   ##
=======================================
  Coverage   60.40%   60.41%           
=======================================
  Files         245      245           
  Lines       31063    31063           
=======================================
+ Hits        18764    18767    +3     
+ Misses      10629    10628    -1     
+ Partials     1670     1668    -2     

Files with missing lines	Coverage Δ
blockservice/blockservice.go	78.23% <100.00%> (ø)
blockstore/blockstore.go	57.97% <0.00%> (ø)

... and 11 files with indirect coverage changes