integrate metagenomic workflows

bc theyre cool, interesting, relevant, and at least one person has asked for it lol

mocks start from idea of putting all types of workflows in a single top menu item together.

stepper probably looks different, and i guess itd be galaxy managing ref dbs? i also imagine the ref db step optional for some, or maybe most workflows if only one option makes sense/ is supported for ex.

important to note here, looks like we might already have some relevant workflows in iwc. so this is maybe also short term actionable.