DM-40798: Exclude sky sources from RB classification

[rai-harshit]

Create a new pipelineTask that selects sources from the diaSource catalog and writes a goodSeeingDiff_candidateDiaSrc (or similar name) catalog that can be used as an input to TransiNetTask.

[isullivan]

I'd like to see fairly substantial changes in this package, so I would like to re-review after you have addressed my current comments.

[isullivan]

I forgot to add in my initial review a request to deprecate the config doRemoveSkySources in TransformDiaSourceCatalogTask, and remove the code that handles sky sources around line 226 of that file. Instead, you could add a check to see if any sources are flagged as sky sources, and either raise an error if any are found.

[isullivan]

Looks good! I have a few straightforward comments, mostly to make your code style match LSST standards.