Add `ref.semverFilter` to `OCIRepository` API

[stefanprodan]

To cope with the semver range limitation where it's not possible to select only pre-releases, I propose we introduce regex filtering capabilities similar to what we have in ImagePolicy.

Example of selecting only pre-releases:

apiVersion: source.toolkit.fluxcd.io/v1beta2
kind: OCIRepository
metadata:
  name: podinfo
  namespace: default
spec:
  interval: 5m0s
  url: oci://ghcr.io/stefanprodan/manifests/podinfo
  ref:
    semver: '>=1.0.0-0' # select latest version stable and pre-releases
    semverFilter: '.*-rc.*' # include only release candidates