Minor updates to support model submission form development

• Added --model_repository option to the integration-service-manager CLI
• Preload models from the model repository into the service manager registry
• Added validation_command option to model schema that can be used to validate a run on completion via the 'validate' runner option
• Added dependencies and additional_dependencies options to model schema that can be used to specify packages that should be installed for a model
• Refactor registration to use constants to prevent failure on circular import and speed up import time
• Migrate constants into the constants module
• Fix various bugs introduced by updates to GHA images and dependencies by pinning or updating use (e.g. jsonschema, libroadrunner, mac version, R version)