APIv3: return permissions expandable field on projects

[humitos]

Add ?expand=permissions to project list/detail API endpoints.

Related readthedocs/ext-theme#128

[humitos]

@agjohnson I think we want to move away from expandable fields because it's pretty complex. So, we may not want to use this PR at all -- cc @stsewd

[agjohnson]

What is the complexity here? This PR is very useful in removing the page load time on project/organization/build listings.

If we aren't using expand fields, what other options do we have here for returning this data in a single API request? Does this need to be a second API request from the dashboard?

[stsewd]

This field is specific to the current user, so it shouldn't be a problem. But be aware that this will probably add lots of querysets when listing projects...

[agjohnson]

Good point, I am only using this in the detail view. If there is a way to only allow this expansion on detail views, I think that should be enough as well. Or we can monitor this and see if it is ever used/abused. This should never be documented for users, though it is in a public request that users can inspect too.

[agjohnson]

Do we need to do anything additional with this PR? This feels like a fairly small change, as are the changes to use this in

• Improve page load performance on listing views ext-theme#404

[humitos]

I'm not 100% sure about where we are regarding the expandable fields and this comment from @stsewd. I'm happy to add some test cases to this PR and mark it as ready for review after that if that's the required work here.