Add support for digest image references #51
Description
The input image reference currently requires a tag and does not accept a digest.
Example error with version 0.3.1 on linux:
dcp icr.io/cpopen/ibm-iam-operator-bundle@sha256:c63fdfbbeb3314d3ee889bee86139aa0bf6dd4a69f7e63139b6608abae0b3e5 -c manifests
DEBUG dcp::image > 📦 Searching for image icr.io/cpopen/ibm-iam-operator-bundle@sha256:c63fdfbbeb3314d3ee889bee86139aa0bf6dd4a69f7e63139b6608abae0b3e5 locally
Error: ❌ error pulling image: error 400 Bad Request - invalid reference format