Build JSON API changes

New compare_components plugin is used to ensure different platforms have a common set of components installed
squash plugin now takes save_archive to control creation of squashed image archive.
New remove_worker_metadata plugin which ensures that worker ConfigMaps are now removed after the build

Bug Fixes

'tags' field in Koji build 'output' metadata includes the worker's platform-specific unique tag when group_manifests=true
'repositories' field in Koji build 'output' metadata includes by-digest pull specifications for each pullable object tracked in the registry; for Docker distribution registries this is only the schema 2 digest, but for Pulp this may be both the schema 1 and schema 2 digest
pulp_pull plugin's image ID from pulling the image is used regardless of platform name; this only applies to installations using Pulp < 2.14
import_image reads primary tags from either tag_conf or worker builds annotations
koji_promote saves media types list and koji_parent_id to koji metadata same as koji_upload

koji_import will add the ID of parent image's koji build to metadata.
Documentation updates
docker_api build plugin will provide explanation when build api call fails.
Support for building Flatpaks has been added
add_help plugin now creates man page header fields from the name and maintainer labels, and the build start time
import_image does not explicitly track version-release tags
All requests have timeout set to 10 mins
Layer sizes are now stored in koji metadata
'build-date' label format is in UTC
Metadata for Koji builds will indicate whether or not a build is isolated: extra.image.isolated
flatpak dependencies are now in a separate file