refactor: move references to Ansible Vault variables out of the actual code, provide sane defaults and overwrite those with the values from the Vault. This is done to improve documentation of the interface used with this role.

refactor: restart Apache by flushing handlers instead of registering a variable and checking for changed status

fix: use ANSIBLE_VAULT_PASSWORD_FILE instead of ANSIBLE_VAULT_IDENTITY_LIST in Gitlab-CI config, as it interferes with Molecule

feat: disable CallasPDF based Validation Service in favor of official VeraPDF based Validation Service hosted on SLUB's website

Resolve "CI pipeline can't find Vault password file..."

Closes #1

See merge request !1

test: provide external access to Apache webserver through tcp/8080 for running  tests on the VM host's browser