sap_vm_provision: Hard dependency on AP4S

[marcelmamula]

@sean-freeman sap_vm_provision role is currently directly linked with AP4S and it cannot be executed separately.

common/set_ansible_vars.yml requires all AP4S variables to not fail set_facts, but they are not documented anywhere as requirement.

Proposal:

1. Uncouple both repositories by giving optional variable that would allow to use this role separately.
2. Update Readme to say it cannot run without AP4S

   community.sap_infrastructure/roles/sap_vm_provision/README.md

   Line 7 in a67f6b8

   Primarily, this Ansible Role was designed to be executed end-to-end (i.e. Provision host/s, configure OS for SAP Software, install SAP Software, instantiate the SAP System); such as the [Ansible Playbooks for SAP](https://github.com/sap-linuxlab/ansible.playbooks_for_sap).

[sean-freeman]

Closed by PR #6