Feature to populate and manage task:configuration collections

User story

As a workspace owner, I can manage the content of the task:configuration collection(s) available in the workspace.

This needs to be refined but we basically said this:

• we want something on the API and debusine-client side, knowing that Debian would likely want to manage this over git, and that we should provide some interface that doesn't make it too hard to create the required glue.
• we probably want some Web UI where we can provide "subject/context" and get back the merged configuration data that would be provided for the work request

Error handling

Describe the various error/failure scenarios and the expected behaviour.

Implementation plan

Fill in this section with a rough plan of how the feature will be implemented in the code base. This does not have to be filled from the start but should be filled before writing any code. For larger changes, it might be wise to first write official design documentation. In those cases, you should put here links to the corresponding documentation once it has been merged.

Open questions

• Add any question that needs to be resolved before proceeding with implementation

Notes

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

Q2 review / Q3 planning

Still missing:

• Add web UI to look up configuration for a task with a given subject/context
• Support multiple entries in a single YAML file (#968 (closed))