*Update operator-registry dependency to 1.6.0
*Adds fix for generated dockerfiles
*Adds optional output-directory parameter
*Update cleanup funcs to handle new structure

operator-registry image builder but not generated by the SDK.
In case deploy/olm-catalog/<operator-name>/manifests doesn't
exist, create one and delete it after the image is done
building. If --generate-only is set, do not remove manifests/.
--version lets a user specify which operator version they want
to build an image for, and --latest uses the highest semver'd
operator in the bundle parent dir.

hack/tests: add 'bundle create' test cases

doc,website: update generated CLI docs

CHANGELOG.md: --output-dir addition and breaking change for bundle.Dockerfile location

doc/migration: add breaking change to migration guide