feat(W-17752806): Pipeline creation must support the generation property

[justinwilaby]

Adds the --generation flag to the command.

To Test

1. Test per usual but use the --generation flag. Try good and bad values, try 'fir' on cedar apps and 'cedar' on fir apps, etc..
   W-17752806

[eablack]

There are a few issues here:

1. Happy path doesn't work. When I run the command, I get what appears to be a 500 error:

2. I think we should reconsider how this behaves, maybe talk with @dsouza-anush about it. Right now, the pipelines create command requires an --app flag. Adding the --generation flag means someone can try to create a fir pipeline with a cedar app. The api blocks this, thankfully, but we should stop this from happening earlier. My recommendation is we do one of two things:

• Keep --app as a required flag and just pass the generation of that app when we do the API call to create a pipeline. If we do this, we do not need to offer generation as a flag option. I think this is the simplest solution.
• Make '--app' an optional flag and add --generation as a flag and let the user possibly create a pipeline without an app. We probably should check to make sure in the CLI that there isn't a conflict between the --generation value and the app's generation if the user does provide an app.

[justinwilaby]

I am working with @bchen528 on this 500 error. It does seem to be a backend issue related to this line.

Originally, I thought this was because the fir app I was using to test was deployed using the BuildService and not git push heroku main.

I'm not really sure why this flag is necessary. The call succeeds and the pipeline API correctly infers the generation without this flag present. There are almost no details in the ticket on this so my assumption was this flag would allow both fir and cedar apps on the same pipeline potentially for migration from cedar to fir on the same pipeline.

[justinwilaby]

Moving this to draft until then.