Adds a bearer token middleware that adds support for tokens prefixed
with "Bearer" scheme. Prefixing with "Bearer" is optional and the old
way of authenticating still works, so we now support both ways.
Also, added as part of our OpenAPI spec which now displays authorization
as follows:
Related to #4630. Doesn't fully close the issue as we're still using
some invalid characters for the RFC, in particular `*` and `[]`
For safety reasons this is behind a feature flag
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Co-authored-by: Gastón Fournier <gaston@getunleash.io>
