Migrate historical pipeline plugins

The apizr.pipeline.v1 entrypoint group, PipelinePlugin, step engine and --plugin generation hook were removed in 0.4.6 along with the legacy pipeline. Installed historical extensions no longer activate through Apizr. There is no automatic conversion of a mutable pipeline hook into a trusted extension.

Package explicit operations with the current extension protocol and the plugin guide. Scientific recognizers can use the provider contract. An application build step that transforms files should remain an explicit, reviewed build command outside Apizr's evidence contracts. See the migration table.