Inspection caching is partially implemented and bypassed as in https://issues.redhat.com/browse/MIXEDARCH-328

The cache was disabled in https://github.com/openshift/multiarch-tuning-operator/commit/1679c05e97abe09c94f163fbde91cce46a06d4f5 because it has no eviction policy and can lead to leaking metadata for consumers that shouldn't be able to access a given image's metadata and even pull it.

Acceptance criteria:

1. An eviction policy for the cache is considered. The current implementation fill the cache for each MISS, and never evict entries.

Nice to have:

1. expose cache size as a prometheus gauge

Cache eviction policy

We can use https://github.com/hashicorp/golang-lru, following the last example in the readme, capacity 512, TTL 4hr.