Share projects with groups

[infkf]

Description of your changes

Fixes #270
Adds ProjectShareGroup instance to work with projects and groups

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

• Unit test has been added
• CRUD operations working locally

[henrysachs]

@infkf is this ready for review?

[henrysachs]

H1: Update() should delete+create atomically

Update() only calls Delete() and relies on the next reconcile to re-create. This leaves the share removed for up to one poll interval. Existing controllers (ldapgrouplinks, protectedbranches) do delete+create within Update():

func (e *external) Update(ctx context.Context, mg resource.Managed) (managed.ExternalUpdate, error) {
    if _, err := e.Delete(ctx, mg); err != nil {
        return managed.ExternalUpdate{}, err
    }
    _, err := e.Create(ctx, mg)
    return managed.ExternalUpdate{}, err
}

H2: Nil pointer dereference in Create() and Delete()

ProjectID and GroupID are *string + +optional. Observe() guards against nil, but Create() and Delete() dereference them directly (*cr.Spec.ForProvider.GroupID). If reference resolution fails, this panics. Other controllers (members, badges) guard these — please add nil checks.

H3: Observe() doesn't handle 404 from GetProject

Response is discarded (_), so 404 can't be distinguished from auth/network errors. If the referenced project is deleted externally, this causes an infinite retry loop instead of gracefully reporting the resource as absent. Every other controller captures the response and checks clients.IsResponseNotFound(res):

p, res, err := e.client.GetProject(...)
if err != nil {
    if clients.IsResponseNotFound(res) {
        return managed.ExternalObservation{ResourceExists: false}, nil
    }
    return managed.ExternalObservation{}, errors.Wrap(err, errGetProject)
}

[infkf]

@henrysachs Please take another look

[henrysachs]

@infkf could you please sign the dco so i can also compare it in ci?

[infkf]

@infkf could you please sign the dco so i can also compare it in ci?

done