feat: Add default stack flavours

[slothkong]

Hello again @xavierabellan

This is the follow up PR we promised to publish default stack flavours.

What's new?
Ansible Playbooks for configuring :

1. existing RockyLinux instances to serve as an SSH proxy server (good-old SSHD flavour)
2. existing RockyLinux instances to serve as remote desktops (X2Go flavour)
3. existing RockyLinux instances to run as IPA servers (FreeIPA flavour)
4. existing RockyLinux or Ubuntu instances to run IPA client and enroll into IPA servers (also FreeIPA flavour)
5. existing and enrolled RockyLinux or Ubuntu instances so that they disenroll from IPA servers
6. new RockyLinux or Ubuntu to enroll/disenroll to/from IPA servers during Murpheus Workflow provisioning and teardown phases.

Additionally:
7. new references to the required Ansible Roles (pending for release and currently under EUMETSAT quality assurance review)

What stays the same?
Self-provisioning Ansible Playbooks (i.e. Terraform under the hood) are kept out of the PR, as you voiced concerns that sort of items go beyond the scope of this repository.

Is this PR worthy of a new release branch?
Yes, a feat: prefix on the squash-merge operation is advised so that we go into 2.1.0

[slothkong]

cc: @pacospace , @ecusrc

[slothkong]

@tervo I am closing this PR based on your remarks from today, as it is unclear on our side what is considered a "contribution" to and "ownership" of a EWC-supported Item in the context of the Community Hub.