[UNREAL/CLI] Enable smooth transition between UBeamEnvironments

[PedroRauizBeamable]

In order to support:

• Private Cloud Customers
• Our own internal ability to run the backend locally
• Our own sample release pipeline.

We need to do a few things in the CLI:

• Make the CLI store its connection configuration Per-Env.
• Allow swapping the environment seamlessly via a command.

In UE, we should then:

• Make the Environment be something like the TargetRealm -- where, in the Editor, it is set and read from the CLI; but in builds, it is baked into the ini file.
• This would no longer be Data Asset based; which means we'd need to solve the "when we install this, where to we put the default" and the "how do we update the version value of the SDK on upgrade".

There's still some foggy details on how to make this work, but... we do need to solve this.

[PedroRauizBeamable]

We ended up making this at the UE-level ---- after internal discussion, the CLI would mostly remain the same short of the changes to the .beamable folder structure defined here beamable/BeamableProduct#4403.