refactor: use the yml extension for every yaml file

The repository mixed both extensions, the molecule scenario used yml while the role itself used yaml. The yml
extension is the one ansible-galaxy and molecule generate and the one the sibling roles use, so it is applied
throughout.

The first_found lookups in tasks/main.yml name the candidate files explicitly and were adjusted accordingly, otherwise
the role would no longer find its distribution variables and its verification tasks.

Co-authored-by: Copilot <copilot@github.com>

meta/argument_specs.yml

@@ -0,0 +1,17 @@
+---
+argument_specs:
+  main:
+    short_description: "Role to configure sudoers on different distributions"
+    description:
+    - "This Ansible role installs sudo and manages drop-in files in /etc/sudoers.d."
+    - "Each drop-in file grants a unix user or a unix group the permission to execute commands, optionally as another
+      unix user."
+    author: "Markus Pesch"
+    options:
+      sudo_users_sudoers:
+        description:
+        - "List of sudoers drop-in files. Each entry must define either 'user' or 'group', but not both."
+        - "Supported keys are 'commands', 'filename', 'group', 'nopassword', 'runas', 'state' and 'user'."
+        type: list
+        elements: dict
+        default: []