Allow assigning to users in Accountability module

Is your feature request related to a problem? Please describe.
The accountability module exists to:

allow(s) people to follow project implementations. It works like a project management system built into the platform.

Currently, across all the aspects of the Accountability module, there's no way of assigning projects, results or timeline entries to a specific individual and/or group, such that people are aware of the status of tasks and the person who is responsible for actioning them.

In our case, we're looking to use this to track the onboarding of new contributors in our open source project, so we'd like to be able to assign each step to the specific person meaning that it's clear who's responsible at any point of the contributor journey.

Describe the solution you'd like
I would like to be able to assign at each level, a responsible person. This would use the Decidim user select field, I imagine, and associate that person to that project/result/timeline/task.

Describe alternatives you've considered
Currently I'm using timeline entries to show what's expected to happen when and putting the name of the person in brackets after the title:

https://nimb.ws/oU1EQln

I also tried doing the same with creating results (but this seemed slightly overkill for what we want to achieve).

Additional context
We have a fairly niche use case but I would imagine anyone who is using this in a project-management setting, even at a basic level, would value being able to set who is accountable for each step of the project.

Does this issue could impact on users private data?
I don't think so, other than surfacing the accountable user's username as it would across any other area of Decidim.

Funded by
Does not currently have funding.