campaigns: Changeset resolver now uses derived fields

Created by: ryanslade

Also, see first commit for interesting bug.

Created by: codecov[bot]

Codecov Report

Merging #8986 into master will decrease coverage by 0.01%. The diff coverage is 61.53%.

@@            Coverage Diff             @@
##           master    #8986      +/-   ##
==========================================
- Coverage   41.62%   41.61%   -0.02%     
==========================================
  Files        1314     1314              
  Lines       70832    70823       -9     
  Branches     6556     6556              
==========================================
- Hits        29487    29472      -15     
- Misses      38656    38664       +8     
+ Partials     2689     2687       -2     

Impacted Files	Coverage Δ
cmd/frontend/graphqlbackend/campaigns.go	0.00% <ø> (ø)
internal/extsvc/bitbucketserver/client.go	49.90% <28.57%> (ø)
...erprise/internal/campaigns/resolvers/changesets.go	54.20% <100.00%> (-4.54%)
internal/campaigns/types.go	23.02% <100.00%> (ø)