cephadm: add deploy-from command

cephadm: add deploy-from command

Add the `deploy-from` command. This command is like `deploy` in
functionality but instead of sourcing input from a mixture of various
CLI arguments, CLI arguments that take JSON strings, and JSON data
provided on stdin - this command aims to take configuration from a
single unified JSON object provided on the commands stdin.

This change strives to be as reasonably backwards compatible with
`deploy` as possible and this leads to some awkward hoop-jumping,
including: needing to nest CLI arguments inside the JSON, because
that is what the manager constructs; duplicate sources of the fsid
(CLI and JSON); the strange behavior of CephadmContext when setting
values; and a few others I'm probably forgetting.

Signed-off-by: John Mulligan <jmulligan@redhat.com>