feat(http, new_relic): handle new_relic error from the PHP worker

[rustatian]

Reason for This PR

• txn.NoticeError(err) support.

Description of Changes

• Handle txn.NoticeError(err) errors.

New Relic errors from the PHP are handled by the special HTTP header - rr_newrelic_error. Predefined values:

• message:foo - Redirected message (string).
• class:bar - Redirected error class (string).
• attributes:baz - Redirected error attributes (string).

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.] [Reviewer TODO: Verify that these criteria are met. Request changes if not]

• [x] All commits in this PR are signed (git commit -s).
• [x] The reason for this PR is clearly provided (issue no. or explanation).
• [x] The description of changes is clear and encompassing.
• [x] Any required documentation changes (code and docs) are included in this PR.
• [x] Any user-facing changes are mentioned in CHANGELOG.md.
• [x] All added/changed functionality is tested.

[codecov[bot]]

Codecov Report

Merging #94 (9320a95) into master (2cfc2da) will decrease coverage by 0.81%. The diff coverage is 52.94%.

@@            Coverage Diff             @@
##           master      #94      +/-   ##
==========================================
- Coverage   68.57%   67.75%   -0.82%     
==========================================
  Files         118      123       +5     
  Lines        9947    10099     +152     
==========================================
+ Hits         6821     6843      +22     
- Misses       2454     2582     +128     
- Partials      672      674       +2     

Impacted Files	Coverage Δ
http/middleware/new_relic/plugin.go	0.00% <0.00%> (ø)
http/middleware/new_relic/splitter.go	80.00% <80.00%> (ø)
http/middleware/new_relic/error.go	100.00% <100.00%> (ø)
boltdb/boltjobs/listener.go	58.49% <0.00%> (-2.84%)	:arrow_down:
sqs/sqsjobs/item.go	65.78% <0.00%> (-1.32%)	:arrow_down:
http/middleware/new_relic/writer.go	0.00% <0.00%> (ø)
http/middleware/new_relic/config.go	0.00% <0.00%> (ø)

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