Allow running tests through the CLI and display the output

[ewanharris]

We want to allow developers to run their store based tests from within the extension, there are a few ways we can approach this and they are mostly building on top of each other to get to the best experience we can provide, however the latter stages do require changes to the CLI to facilitate this integration.

Command Palette

We introduce a new command that developers can run via the Command Palette (similar to our existing transform command), this command could either:

• Create a new terminal that runs the fga model test command
• Run the fga model test command in the background and log the output to an output channel

This should be the first pass at this feature that allows us to gather feedback and see how developers use the feature.

Test Explorer Integration

In future, we could look to add integration with the Testing API that would allow developers to run their tests from the the Test Explorer view. This would require:

• Updating the extension to declare we contribute this feature
• Handle creating the test representations in VS Code when we parse the store file
• Amending the above feature to run the tests as required and reporting back the failures/successes

It would also most likely require the following from the CLI:

• A better "machine readable" output format for testing so that we don't have to rely on regex's
• Ability to run single tests