Activate caching of images and bundles

[joaopapereira]

What this PR does / why we need it:

In this PR kapp-controller will start to cache images and bundles. This feature will allow kapp-controller to reconcile pre-existing applications and package repositories even if the registry is no longer available. This only happens when the images/bundles are referenced by SHA and in the case of bundles if all the images are colocated.

Which issue(s) this PR fixes:

Fixes #664 Fixes #688 Fixes #689

Does this PR introduce a user-facing change?

Allow `kapp-controller` to keep working even if the image registry is no longer available. This change also lowers the number of requests that `kapp-controller` needs to do to the registry, decreasing the load in these registries. 

Additional Notes for your reviewer:

Review Checklist:

• [X] Follows the developer guidelines
• [x] Relevant tests are added or updated
• [x] Relevant docs in this repo added or updated
• [x] Relevant carvel.dev docs added or updated in a separate PR and there's a link to that PR
• [X] Code is at least as readable and maintainable as it was before this change