Allow plugins to save assemblies to samples

[tom114]

Describe your idea for a new feature

Allow irida pipeline plugins to save assemblies to a sample. Currently the only pipeline that can save an assembly is the built-in assembly & annotation pipeline. It would be useful if plugins could also save assemblies.

Describe how you would access this feature?

This would mostly be a developer feature. Developers need access to the genome assembly service to save assemblies which would need loaded into their updater classes.

Additional information

Initially from a question from @dfornika on Gitter.