Update documentation in accordance with the new cloud plugin

[kate-goldenring]

Add documentation on how Fermyon Cloud related commands are a part of a cloud plugin that is either automatically installed via the install script (todo), distributed with Spin via a package manager, or installed in the first invocation of spin cloud (or aliased spin login or spin deploy):

$ spin deploy
The `cloud` plugin is required. Installing now.
Plugin 'cloud' was installed successfully!
Uploading cloud_start version 0.1.0+XXXXXXXX...
Deploying...
Waiting for application to become ready... ready
Available Routes:
  cloud-start: https://cloud-start-xxxxxxxx.fermyon.app/ (wildcard)

Here is the current PR to move to using the plugin: fermyon/spin#1452

cc @tpmccallum

[tpmccallum]

Thanks @kate-goldenring I will take a look.

[kate-goldenring]

looks like spin doctor was added so ill add a section on that

[itowlson]

spin doctor is hidden in 1.2. It got merged into main so a wider group can iterate on it, but is not yet surfaced to users and should not be included in 1.2 docs.

[kate-goldenring]

sorry i meant to add this comment to the release blog -- will start a thread there

[itowlson]

@kate-goldenring Closing as you did this in a couple of PRs around the 1.3 timeframe - feel free to reopen if there is more to do!