lxd: Add support for forced deletion of projects

[boltmark]

Currently in draft state as this PR relies on deleting resources via requests to the server's own API. This is not ideal, and I am investigating if it is possible to avoid this. Right now it looks like this is the simplest option, but we could likely add implementation for each resource to perform the deletes without invoking the LXD API. Perhaps we could factor out some of the logic in the delete handlers so that we can reference it locally. Still looking into this -- WIP.

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This PR adds support for forced deletion of projects. If the --force flag is provided when attempting to delete a project, and if the user confirms that forced deletion is what they want, then all resources associated with the project will be deleted and the project will be removed.

This PR also simplifies the projectIsEmpty function to utilize projectUsedBy instead of checking each resource manually.

Includes cherry-picks from lxc/incus#900.

Closes: #14316.

[github-actions]

Heads up @mionaalex - the "Documentation" label was applied to this issue.

[tomponline]

@markylaing this is the PR I mentioned earlier wrt to doing loopback client requests, not @kadinsayani PR in the end. Apologies for confusion.

[markylaing]

Wow this is a headache to read but I think I understand the reasoning. We want to use existing code to perform the deletion and not to reimplement any logic in the deletion handlers. We still want the handlers to perform all of their internal logic (e.g. forwarding storage volume/bucket requests to the member containing the volume and so on).

This is an example of where it would have been useful to have a design pattern in out API endpoints (such as MVC) where request parsing is separated from business logic.

As it stands I think this can be improved in the following ways:

1. Get the project used by list.
2. Parse this list entries with entity.ParseURL and categorise them.
3. For each entity type, iterate over the entities, and create a *http.Request and call the appropriate handler with it.

We should also consider the features configuration on the project here. Force deleting a project should delete any networks in the default project.

[markylaing]

@boltmark also could you please add some tests for this. Thanks :)

[boltmark]

Hi @tomponline, looping you into this question I had --

I'm facing a bit of an issue invoking deletion endpoints locally with dummy requests. Mainly, we currently seem to rely on everything going through the HTTP request routing/handling since we need mux to inject variables into the request context. For example, we expect to be able to access these mux vars here: https://github.com/canonical/lxd/blob/main/lxd/network_acls.go#L311.

I'm able to inject mux vars into the dummy requests via mux.SetURLVars, but this function is pretty explicit about only being there for testing purposes. Am I missing something here? If not and this is in fact an issue, is some sort of refactoring of endpoints worth it for this?

CC @markylaing