Generalize req/res body redaction

[john-odonnell]

Desired Outcome

DRYing this up. redactRequestBody and redactResponseBody did a lot of the same stuff, but I couldn't set up a generic type to represent them both.

Implemented Changes

Instead of running body redaction logic against *http.Request and *http.Response objects, operate against pointers to their ReadCloser bodies and int64 content-lengths.

Connected Issue/Story

N/A

Definition of Done

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Behavior

• This PR changes product behavior and has been reviewed by a PO, or
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• No behavior was changed with this PR

Security

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[szh]

LGTM 👍

[codeclimate]

Code Climate has analyzed commit 78ce00c and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 82.2% (0.0% change).

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