Add schema checks of task-maps

[lbradstreet]

The task map entries are getting more complicated over time, and we're having to add validation for kvs that are changing between versions. We should add a schema check for task maps entries to make this process easier.

Schema checks should be relatively non-strict, i.e. they only check the keys and values that are known about by the plugin, and ignore any additional keys.

[gardnervickers]

I believe this is solved with task bundle schemas.

[lbradstreet]

This is still relevant as not all users will be using task bundles. Leaving open for now, but it is not currently a priority until ABS is here and we redo onyx-kafka.

[lbradstreet]

Done in master.