Add OpenStack plugin

[dmbuil]

Overview

• Add a new shell plugin for OpenStack CLI. It supports the official Python-based openstack CLI, as well as Rust-based osc CLI.
• Credentials are provided by means of the OS_ env vars.
• Credentials can be imported from the usual OpenStack sources:
  • Environment Variables.
  • openrc.sh file on current path
  • clouds.yaml file, in any usual location. It also parses the secure.yaml file, if available.
• OS_AUTH_TYPE is set automatically at provision time:
  • v3applicationcredential: when OS_APPLICATION_CREDENTIAL_ID is present. OS_USERNAME and
    OS_PASSWORD are stripped to avoid conflicting parameters.
  • password: otherwise.

Type of change

• Created a new plugin
• Improved an existing plugin
• Fixed a bug in an existing plugin
• Improved contributor utilities or experience

Test Plan

• make openstack/validate: all checks pass
• make test: openstack tests pass (17 scenarios covering provisioner, importer, and NeedsAuth)
• make openstack/build: builds and installs locally
• op plugin init openstack: end-to-end verification (requires 1Password CLI)
• openstack token issue for validation