Track dependencies on environments

[arunkumar611]

Today, users can update and delete environments without knowing that they are imported into other environments and Pulumi stacks.

We need to track the downstream environments and stacks and surface them to the user.

Must have:

• Simple Table listing the dependencies/relationships(1 level up/down) within each Environment (list which versions of the environments are being used where)
• List the dependencies when users delete the environments
  • Should we also warn when making updates?
  • Should we prevent users from deleting an environment until they remove the dependencies?
• Show on the stacks page, which environments are used
• Ability for users to query
  • "List all environments that don't have a downstream dependency"
  • Add metadata tags to environments (example: NoOfDownstreamEnvs, Is-imported)

Should have:

• Multi-level dependencies:
• Ability to query "list all environments which don't have any imported environments" via the UI and CLI

Nice to have:

• Visualization of the dependencies