Update generic nodes to use static icon api

[ajbozarth]

Currently generic nodes still use encoded strings of the LabIcon svgs.
This PR adds copies of those svgs to the backend static API and
updates the pipeline editor to use those for the persisted values,
like we already do with kfp and airflow nodes.

Fixes #2907

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[akchinSTC]

running front end integration tests to regenerate snapshots are failing, might need to look into it as substask

[karlaspuldaro]

This looks good to me! Only didn't get a chance to test it locally, although we cover icons in integration tests :)