fix: replace empty group list with create modal

[Ph4t3]

When there is no group yet for the organization, instead of showing an empty group list, the modal for Create Group is already rendered inline.
Adjusted e2e tests to cover these two different states.

Still a draft, cause instead of having the form twice in the page, gonna pull it out into it's own component.

Also, the styling is bad when the modal covers the whole width, so there is some empty space on the right, which could be used for a flowchart explaining the organization-group-project structure.
We know from the usability test that some users were confused having to set up a group after just having created an org already. The Organization page also has the lanyard animation on the right side upon new org creation, so similarly a flowchart that already contains the org name one is inside of, and adding the group name live while typing it in the Create Group modal, could be a great way to onboard users and make the structure easier to understand.

Gonna convert from draft after:

• Make Create Group form reusable
• Structure Flowchart on the right

Resolves l3montree-dev/devguard#2716