authorize: decode CheckRequest path for redirect

[calebdoxsey]

Summary

The envoy CheckRequest HTTP path comes in encoded:

path (string)
The request target, as it appears in the first line of the HTTP request. This includes the URL path and query-string. No decoding is performed.

So we need to store it as the RawPath instead of the Path.

Related issues

Fixes https://github.com/pomerium/internal/issues/468

Checklist

• reference any related issues
• updated docs
• updated unit tests
• updated UPGRADING.md
• add appropriate tag (improvement / bug / etc)
• ready for review

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[coveralls]

Coverage decreased (-0.2%) to 64.421% when pulling d813d45 on cdoxsey/468-path-escape into 8973735 on master.