[FEATURE] Support rate limiting of APIs

[dogawaf]

While integrating Twitter API v2, I was facing quite a restrictive rate limits:

• https://developer.twitter.com/en/docs/twitter-api/rate-limits
• https://developer.twitter.com/en/docs/twitter-api/tweets/timelines/api-reference/get-users-id-tweets

Twitter's documentation is not accurate and mention limits that are not observed in the real life. For example, with a Basic tier, I was expecting a 1500 requests / 15 min for the timeline endpoint, but in fact, the limit is 10 requests / 15 minutes!

Anyway, I've implemented a rate limiting support for Twitter v2 into the extension, in order to get the right numbers from the response's headers, and to pause the import task until the rate limit get reset.

See the attached patch:
pxasocialfeed_retry_429.patch.txt

It offers a generic way for integrators to hook into the error handling during the import of a feed.
Then, a new exception can be returned in order to retry the import, with a hard limit of 5 retry.

Here is an example of the slot handling the rate limiting of Twitter v2:
ImportFeedSlot.php.txt

If the approach is good for you, I can make a pull request.

[MattiasNilsson]

@dogawaf This looks great and I would appreciate a PR :)