[issue2551263] Expose headers via rest and Access-Control-Expose-Headers header

New submission from John Rouillard:

Currently none of the rate limiting headers are available to a rest client.

Have roundup return an 'Access-Control-Expose-Headers' header with at least the following 
value:

X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset, X-RateLimit-Limit-Period, Retry-
After, Allow, Sunset

This includes all the rate limit headers to throttle requests.
The allow header so it can determine how to query the endpoint.
The sunset header so it can see if it's using a deprecated API endpoint.

Ref: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Expose-Headers

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components: API, Web interface
messages: 7726
nosy: rouilj
severity: normal
status: new
title: Expose headers via rest and Access-Control-Expose-Headers header
type: rfe

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Roundup tracker <[email protected]>
<https://issues.roundup-tracker.org/issue2551263>
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