Track processed images via Annotations

[ckotzbauer]

Currently with git as the only target it is possible to only analyze images with digests which are not available in the git-repository yet.
With additional targets (e.g. Depdency Track) this is not (easy) possible anymore.

Suggestion:

1. Add annotations to pods for each container-image which already has been processed

annotations:
  ckotzbauer.sbom-operator.io/<containername>: <containerdigest>

A container-image would be analyzed when the annotation for a particular container of the pod is missing or the digest differs from the current container-digest. To force a single image the annotation can be removed manually.

2. Add a operator-flag --ignore-annotations to force analysis for all images (in case that there is a new target configured which has to be populated for the first time). After that the flag has to be removed.

/kind feature