[WIP] Model Store Workflow Invocation Import/Export

[jmchilton]

Early days here still... builds a bit on #9023 (mostly just for a clean diff).

Adds an API endpoint for a version that doesn't include files - this should be quick enough to handle in a web thread. A version that would include files like history export should probably mirror that and I'm not quite sure what the future of history import/export APIs look like. @mvdbeek thinks the jobs should just output the results to a history to simplify a lot of the plumbing and the UI.

Will land up supporting a Galaxy native format that sort of mirrors history exports, as well as bagit packaging.

It is probably a bug that history import/export doesn't include invocation information - this will hopefully fix that issue. Really meant a stepping stone for https://github.com/galaxyproject/galaxy/issues/3088 / https://github.com/galaxyproject/galaxy/issues/2491.