Multiple active deployments & zero downtime assurance

[aleclarson]

• Add saus deploy new to spin up a new deployment instead of updating
• Add prompt to saus deploy that asks which active deployment to update, and if updates should be done in-place or not (ie: spin up a temporary deployment before updating DNS)
• Both of the features above will need support for multiple secret depositories
• Generate a name for each active deployment
  • Probably something like [branch]-[commit]
• Add saus deploy ls for listing active deployments
• Add saus deploy rm [name] for destroying a deployment (with confirm prompt)
• Add saus deploy rm --all to destroy all deployments