Add persistent license cache

[rainest]

The Konnect license agent needs a local persistent cache of the license in the event that Konnect is unavailable or unreachable. This provides outage resilience, allowing KIC to continue licensing managed proxy instances in the event of an outage and a controller restart.

The persistent cache will likely be a local Secret maintained by KIC. If Konnect is not available, KIC will fall back to reading this Secret and injecting the license cached in it.

[czeslavo]

@mflendrich As we discussed today, this is not something that we need right now, and most probably the initial implementation of licensing will change in the future, making this irrelevant in both cases. Are we ok with closing this?