These changes add the API types and cloud backend code necessary to
interact with service-managed stacks (i.e. stacks that do not have
PPC-managed deployments). The bulk of these changes are unremarkable:
the API types are straightforward, as are most of the interactions with
the new APIs. The trickiest bits are token and log management.
During an update to a managed stack, the CLI must continually renew the
token used to authorize the operations on that stack that comprise the
update. Once a token has been renewed, the old token should be
discarded. The CLI supports this by running a goroutine that is
responsible for both periodically renewing the token for an update and
servicing requests for the token itself from the rest of the backend.
In addition to token renewal, log output must be captured and uploaded
to the service during an update to a managed stack. Implementing this in
a reasonable fashion required a bit of refactoring in order to reuse
what already exists for the local backend. Each event-specific `Display`
function was replaced with an equivalent `Render` function that returns
a string rather than writing to a stream. This approach was chosen
primarily to avoid dealing with sheared colorization tags, which would
otherwise require clients to fuse log lines before colorizing. We could
take that approach in the future.
