Merge Deployments REST API docs into the main Pulumi Cloud REST API docs

[jkodroff]

We have a page for Deployments' REST API reference https://www.pulumi.com/docs/pulumi-cloud/deployments/api/ which is separate from the rest of the Pulumi Cloud API reference https://www.pulumi.com/docs/pulumi-cloud/reference/cloud-rest-api/. We should merge the Deployments REST API into the Pulumi Cloud REST API for consistency.

• First, we should reformat the page in-place so that it looks like the other pages in the Pulumi Cloud REST API:
  • We don't need the Authentication section - that's now redundant.
  • Add an introductory blurb at the top of the page that explains what this part of the REST API does.
  • All the stuff under "Deployment Settings" is analogous to Schema Definitions under "Resource Search" in the main REST API, so that should go last in the page and be titled "Schema Definitions" for consistency.
  • The formatting of the various REST operations should match what we have elsewhere in the rest of the API docs.
• Create a new page called "Deployments" in the main Pulumi Cloud REST API section of the docs. Ensure that it's placed in alphabetical order.
• Any links to the Deployments REST API page should be rewritten to point to the new location.
• The original page should be removed as it's no longer needed.