Support categorization in running the AppHost

[malisancube]

Say you intend to run some or the projects (but not all) in some configuration and have it named. e.g. Backend. Which may contain databases, cache and Apis.

This would make it easier to work with some certain testing (and later possibly deployment scenareos), where you do not want to spin up new services, but have certain services remain running which you test some behaviours. An example would be I may not wany to spin up a new DB and Background service just cause I need to preserve the data I used before.

So effectively its

1. A feature that would allow for run configurations.
2. Deployment configurations. e.g Deploy "Backend to Region 1 gradually/immediate"
3. Run "Integration Tests" configuration

[davidfowl]

Related to #303

[mitchdenny]

Moving to preview 5 for now needs to be more top down on how the UX works.

[davidfowl]

Moving to backlog.