Improve "Favorites" (servers/users)

Hi @jakob,

First, thanks for all the hard work you and your team put into Postico. I find it exceptionally valuable to my work and have been a happy customer for a long time. You've been responsive to emails and overall just a good experience.

In the course of my work, both professionally and personally, I find myself connecting to a lot of databases. What's more, as a lot of best practices will show, using multiple users (roles/passwords) is preferable to having one master root account.

As such, I typically have something along the lines of:
- master (root)
- schema manager (migrations/migrator)
- account per service
- readonly/analytics

And of course, we have read _replicas_ to contend with as well. Needless to say, this leaves my "favorites" directory a bit overwhelming.

I'd like to offer an idea/suggestion. How would you feel about restructuring the favorites window to allow defining servers, and then within those servers, you can define different users/roles that are appropriate for logging in. Perhaps a collapsable UI (like folders in list view), with a selectable default user/pass for logging in. That way, most of the current behavior is maintained (click "Connect" to log in, or select a different user/pass combo specifically.

I've made a desperate attempt at using colors to help bring some sanity to all of this but got to thinking that perhaps by defining one line per server, and then within that, defining users/roles, we might achieve the organization I'm looking for.

I checked out Postico 2—looking cool! Thought perhaps my issue might have been resolved there, but the same interface seems to be present there as well. And finally, I saw that there is some [interest in getting AWS IAM login working](https://github.com/jakob/Postico/issues/377). That ask might benefit from a refactor on servers/users as it could allow you to "object-orient" a user/login class of some sort.

I've attached a photo in hopes that it might help you empathize a bit with my plight.

All the best,

~ Dale

Start by reviewing the current Favorites window and the AWS IAM login discussion in issue #377. Compare the requested server grouping, collapsible user/role organization, and selectable credentials with the existing behavior; done means users can manage multiple logins per server without losing the current connection flow.

Written by the indexing model from the issue text.