Configure workspace inheritance in the Web UI, in the API and in the CLI

User story

As a workspace owner, I can modify the workspace inheritance list either through the Web UI, through the API or with the CLI.

In the Web UI, I can create an ordered list of workspaces among:

• the workspaces from the current scope that I have access to
• all the public workspaces from other scopes
• the workspaces that are already in the inheritance list (in case they have been added by someone else that had broader access than me)

Error handling

• The API refuse to add private workspace from other scopes in the inheritance list
• The API fails for non-existing workspaces

Implementation plan

• Add the API (!2115 (merged))
• Add the Web UI (!2143 (merged))
• Add the CLI in debusine-client (!2157 (merged))

Open questions

• Should the API work with workspace IDs or with fully qualified names of workspaces (e.g. debian/developers) or accept both interchangeably?

Notes

This issue description can be modified to integrate feedback from comments and from associated merge requests.