feat: Ability to use Flutter Version Management (FVM) with Dart Frog

[Schamppu]

Description

In order to easily handle Flutter and Dart versions when working with multiple developers, environments and flavors, being able to use Dart Frog with FVM would be very helpful. This also helps when:

• There are new Flutter/Dart versions available that aren't yet supported by Dart Frog, but we use locally on different projects.
• When working with multiple flavors or branches locally, some of which use a previous version of Flutter/Dart.
• When deploying servers remotely, to easily manage the Flutter/Dart versions that we want to use.

Proposal:
Being able to use fvm when using Dart Frog CLI commands, such as dart_frog dev and dart_frog build.

For instance, by specifying for the Dart Frog CLI to use FVM configuration instead of the local Flutter version, like:
dart_frog dev -fvm

Or even better, by being able to use the standard way when working with FVM:
fvm dart_frog dev

Requirements

• All CI/CD checks are passing.
• There is no drop in the test coverage percentage.

Additional Context

No response