Add configuration option to allow comment driven ignores for lint

[bufdev]

Fixes #63.

To use:

buf:
  lint:
    allow_comment_ignores: true

Then, in the leading comments for something that will error on lint:

// buf:lint:ignore MESSAGE_PASCAL_CASE
message foo {}

The item will be ignored if any space-trimmed line of the leading comment starts with buf:lint:ignore ID.

[codecov]

Codecov Report

Merging #73 into master will increase coverage by 0.18%.
The diff coverage is 84.84%.

@@            Coverage Diff             @@
##           master      #73      +/-   ##
==========================================
+ Coverage   70.37%   70.55%   +0.18%     
==========================================
  Files         149      150       +1     
  Lines        8202     8266      +64     
==========================================
+ Hits         5772     5832      +60     
- Misses       1807     1811       +4     
  Partials      623      623              

Impacted Files	Coverage Δ
...rnal/buf/bufcheck/buflint/buflintcfg/buflintcfg.go	84.61% <ø> (ø)
internal/buf/bufcheck/internal/checker_builder.go	87.50% <ø> (ø)
internal/buf/bufsrc/protosrc.go	76.41% <ø> (ø)
internal/buf/bufsrc/merge_comment_location.go	60.00% <60.00%> (ø)
internal/buf/bufsrc/named_descriptor.go	81.48% <71.42%> (-4.24%)	⬇️
internal/buf/bufcheck/internal/runner.go	76.92% <75.00%> (-3.85%)	⬇️
...fanalysis/bufanalysistesting/bufanalysistesting.go	100.00% <100.00%> (+2.53%)	⬆️
internal/buf/bufcheck/bufbreaking/handler.go	66.66% <100.00%> (ø)
internal/buf/bufcheck/bufbreaking/internal/util.go	64.88% <100.00%> (ø)
internal/buf/bufcheck/buflint/buflint.go	88.00% <100.00%> (+0.76%)	⬆️
... and 12 more

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