`dotnet watch run` is configurable with regards to its behavior when source changes are detected

[DamianEdwards]

User Story

As a user, I want the behavior of dotnet watch run to be configurable, so that I can tailor what it does when sources are detected to my preferences.

Considerations

• There is already the launchSettings.json file that the CLI and VS use to customize launch behavior. This seems like the logical place to support storing behavior configuration for dotnet watch run at the project level. It would also facilitate setting defaults for new projects via their templates, but not facilitate setting defaults for existing projects (although other ideas could be explored there, e.g. prompting to set the defaults on first launch)
• Should behaviors be configurable via CLI arguments when launching dotnet watch run?
• Some behaviors of dotnet watch run are already configurable via environment variables and/or MSBuild properties/items today. We should consider which configuration values are most suited to each location. Configuration via MSBuild has the advantage of allowing different app SDKs to set defaults with overrides allowed in the project file itself.

[DamianEdwards]

We've done as much here in .NET 6 as we expect to. We can open specific issues from now on for any changes.