ci-operator: add automatic dockerfile inputs detection

[Prucek]

Added pkg/dockerfile/inputs.go - Core detection logic:

• Automatically detects registry.ci.openshift.org and quay-proxy.ci.openshift.org references in Dockerfiles
• Parses references into org/repo/tag components
• Generates base_images and inputs.as[] configuration on-the-fly
• Using registry-replacer's detection logic

Integrated into pkg/defaults/defaults.go:

• New detectDockerfileInputs() function reads Dockerfiles from source checkout
• Calls DetectInputsFromDockerfile() during build graph construction
• Creates input steps that tag detected base images into the pipeline ImageStream
• Respects manual configuration (manual inputs.as[] takes precedence)

Real example config using a mocked prowjob: https://prow.ci.openshift.org/view/gs/test-platform-results/pr-logs/pull/openshift_cluster-api-operator/63/prucek-test-dockerfile-inputs/2009259226555224064