feat: change soft references to clastix.io

[oliverbaehler]

Describe the feature

We can start migrating to projectcapsule.dev from capsule.clastix.io. This is just preparation for a future v1 release. Places i can think of where these references can be changed without big changes:

• Webhook-Names
• Default userGroups
• E2E tests
• Documentation

What would the new user story look like?

How would the new interaction with Capsule look like? E.g.

1. What are the prerequisites for this?
2. Tenant owner creates a new Namespace
3. This is going to be attached to the Tenant
4. All the magic happens in the background

Feel free to add a diagram if that helps explain things.

Expected behavior

A clear and concise description of what you expect to happen.

[prometherion]

Marking this as a breaking change since users must be aware of the renaming of the default user group from capsule.clastix.io to projectcapsule.dev.