feat(license) add expired license behavior

[rainest]

What this PR does / why we need it:

Add new rules for the license agent when the license is expired. The agent will use its initial polling period and disregard updated_at when its cached license is expired.

Add an expired license check helper.

Which issue this PR fixes:

Seeks to fix expired license status quickly, because we want to get out of that state if we're in it. This situation generally should not occur, but could if the controller were unable to talk to Konnect around the same time as its cached license was expiring.

The updated_at behavior is somewhat odd but based on an actual situation where upstream essentially lied about the date and provided a current license with an older updated_at than another expired license it had previously served. There's no use to providing an expired license to the gateway, so we may as well always update cache until we get something that's not expired.

Special notes for your reviewer:

Per comments, the Kong license APIs feature JSON blobs embedded in JSON objects, which is annoying. We can't really properly retrieve license expiration information, though we can probably reasonably expect that it is available at the indicated path. If that expectation breaks, this takes a conservative approach and reverts to expiration-unaware behavior (it updates at the standard interval and relies on updated_at).

The update frequency change is probably always warranted. The change to have expiration supersede updated_at were requested, but I'm less sure of them. There are some unknowns about the incident that suggest they're not actually warranted. See chat discussion for further details.

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

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Additional details and impacted files

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