classify 422 http status as InvalidArgument

[AllenLuUber]

• [x] Description and context for reviewers: one partner, one stranger Currently 422 is marked as unknown and classified as server error. This impacts the server SLA calculation. This diff adds support to classify it as InvalidArgument, a type of client error.
• [x] Entry in CHANGELOG.md

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: +0.01 :tada:

Comparison is base (5b1115a) 85.34% compared to head (42ffecb) 85.36%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #2210 +/- ## ========================================== + Coverage 85.34% 85.36% +0.01% ========================================== Files 270 270 Lines 15479 15479 ========================================== + Hits 13211 13213 +2 + Misses 1845 1844 -1 + Partials 423 422 -1 ``` | [Impacted Files](https://codecov.io/gh/yarpc/yarpc-go/pull/2210?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yarpc) | Coverage Δ | | |---|---|---| | [transport/http/codes.go](https://codecov.io/gh/yarpc/yarpc-go/pull/2210?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yarpc#diff-dHJhbnNwb3J0L2h0dHAvY29kZXMuZ28=) | `100.00% <ø> (ø)` | | ... and [1 file with indirect coverage changes](https://codecov.io/gh/yarpc/yarpc-go/pull/2210/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yarpc) Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yarpc). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yarpc)

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