Add Cloud API support

[Vorlias]

Right now Tarmac is lacking a way to support for the new cloud API, supporting this may allow us to incorporate managing other asset types as well.

My fork had this pull request, it still needs work to incorporate into the project, however. Could perhaps instead use rbxcloud to simplify our internals around Cloud API a bit?

Main functionalities user-side should be:

• It should allow passing API key directly via --api-key argument in the CLI
• It should also allow using environment variable - perhaps TARMAC_API_KEY?
• If an API key is provided or present; use Open Cloud API for uploads otherwise fallback on cookies.