Add guidance on multiple Deployments

[paolaperaza]

Context

Feedback from @ReadytoRocc in Slack that I think is very fair:

Hey Team, do we have any docs/slides on why having multiple Airflow instances in an organization provides benefit? e.g. Isolation of Teams and Processes Reducing interaction of independent processes e.g. 1 team pushes an error which interrupts another team. Ability to create instances for hot-fixes, feature branches, or trying new versions. If not I plan on making some, but wanted to see if this exists already. Thanks!

Ask

In: https://docs.astronomer.io/astro/create-deployment

Let's add a more explicit section somewhere in this doc about how to think about creating multiple Deployments that incorporates some of Rocco's feedback. Will require some internal discussion, but creating a GH issue for now a placeholder that can become actionable once we better define scope.