Show mixed ownership warning

[raulb]

Checklist

The checklist enumerates the tasks you set out to do before the PR becomes ready for review

• Implement feature
• Write tests
• Update CHANGELOG.md

Why

We want to encourage users to set a single ownership model in their pipelines. The metrics around this command proved that it was worth adding a warning message advising them about this situation when proceeds.

This warning is only added to the pipelines:info command as it'd be API expensive to check pipeline coupling ownership in other commands which would slow down the experience considerably.

What are the acceptance criteria for the change?

• DevEx gives a 👍

How can the change be tested

• Download this code

• Run it locally doing heroku plugins:link .

• Run heroku pipelines:info in a pipeline you think it's suspicious of being in this situation.

• enumerate a list of steps that the reviewer may step through to fully experience the changeset being introduced

Demonstration

› heroku pipelines:info my-mixed-pipeline
name:  my-mixed-pipeline
owner: my-team (team)

app name          stage
──────────────    ───────
⬢ one-app         staging
⬢ another-app     staging

 ▸    Some apps in this pipeline do not belong to my-team (team).
 ▸
 ▸    All apps in a pipeline must have the same owner as the pipeline owner.
 ▸    Transfer these apps or change the pipeline owner in pipeline settings.
 ▸    See https://devcenter.heroku.com/articles/pipeline-ownership-transition for more info.

Who's Affected

Users with apps in a pipeline owned by different users/teams.

Blockers & upstream dependencies

None.