Check the argument specification in every role

[afeefghannam89]

We should verify that the variables in the argument specification meta/argument_specs.yml are defined correctly, especially the required and default parameters.

• Variables with a default value should be defined in defaults/main.yml.
• Variables marked as required in the argument specification should not be defined in defaults/main.yml. Instead, they must be provided by the user.

[afeefghannam89]

Consolidated into #495, which now also covers the required/default (argument_specs correctness) audit.

[afeefghannam89]

Reopened: split back out of #495. #495 has grown to cover the internal-variable naming convention and removing internals from argument_specs / defaults, which is enough for one issue. The required / default correctness audit is a separate, orthogonal concern and is tracked here again.

Order: run this after #495, because #495 removes internal variables from defaults/main.yml and meta/argument_specs.yml - auditing first would cover entries that #495 then deletes.

Part of #545.