test: fetch ohttp keys

[ValeraFinebits]

Remove export from fetch_ohttp_keys.
Add OHTTP relay proxy integration test.
As discussed here:
#1351

Pull Request Checklist

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  in the body of this PR.
• I have read CONTRIBUTING.md and rebased my branch to produce hygienic commits.

[coveralls]

Pull Request Test Coverage Report for Build 22371348775

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 82.484%

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Totals
Change from base Build 22262995534:	0.0%
Covered Lines:	10624
Relevant Lines:	12880

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💛 - Coveralls

[spacebear21]

ACK d8c2703

Normally I'd ask to squash your commits, in this case the PR is succinct enough that I'll squash on merge into a single commit. Thanks!