Operator skeleton upgrades

[jacobmarks]

The configs for Python operators have changed a bit since this was created. This PR introduces some minor tweaks to bring the interface up to date.

Still other changes to be made to the @voxel51/plugins plugin, including:

• Adding secrets declaration control to the fiftyone.yml.
• Distinct code for when operator executes as generator, with yield...
• Allow for multiple triggers, in arbitrary order, and using ctx.ops where possible
• Some reference to the docs or the @voxel51/examples plugin so people know other types exist, like str, Tuple, ..., which don't have multiple view type options, but still deserve to be included in this plugin
• if user has selected an icon file for one of the icons, then they should have the option to use this for another icon instead of going through the FileExplorer again.