enhancement: Output detailed index build errors when the number of errors is low

[haines]

Fixes #441

When no more than 5 errors occur during index build, or when debug logging is enabled, the full error details will now be printed instead of just the summary.

e.g. when starting server the output is now

2022-06-21T10:59:32.594+0100    ERROR   cerbos.index    Index build failed      {"missing": [{"importingFile":"policy.yaml","desc":"Import 'wat' not found"}]}
cerbos: error: failed to create store: failed to build index: missing imports=1, missing scopes=0, duplicate definitions=0, load failures=0

or if more than 5 errors occur

2022-06-21T11:38:49.002+0100    ERROR   cerbos.index    Index build failed      {"error": "too many errors; run `cerbos compile` to see a full list"}
cerbos: error: failed to create store: failed to build index: missing imports=3, missing scopes=0, duplicate definitions=0, load failures=3

[codecov]

Codecov Report

Merging #1038 (2becb98) into main (95ceef5) will increase coverage by 0.22%.
The diff coverage is 70.10%.

@@            Coverage Diff             @@
##             main    #1038      +/-   ##
==========================================
+ Coverage   54.73%   54.96%   +0.22%     
==========================================
  Files         106      106              
  Lines       11806    11875      +69     
==========================================
+ Hits         6462     6527      +65     
- Misses       4796     4798       +2     
- Partials      548      550       +2     

Impacted Files	Coverage Δ
internal/storage/index/index.go	38.61% <0.00%> (ø)
internal/engine/ast.go	77.71% <68.00%> (-1.15%)	⬇️
internal/storage/index/builder.go	84.46% <73.91%> (+1.41%)	⬆️
internal/server/tests.go	94.24% <0.00%> (-0.91%)	⬇️
internal/audit/local/badgerdb.go	63.17% <0.00%> (-0.64%)	⬇️
internal/engine/engine.go	63.84% <0.00%> (+0.76%)	⬆️
internal/engine/planner.go	76.97% <0.00%> (+1.16%)	⬆️
internal/compile/errors.go	55.55% <0.00%> (+15.87%)	⬆️

[charithe]

🙌🏽