Clean up module documentation (#36909)

* Clean up module documentation

This PR includes:
- Removal of `default: None` (and variations)
- Removal of `required: false`
- Fixing booleans and `type: bool` where required

* Fix remaining (new) validation issues

lib/ansible/utils/module_docs_fragments/zabbix.py

@@ -38,24 +38,19 @@ options:
     http_login_user:
         description:
             - Basic Auth login
-        required: false
-        default: None
         version_added: "2.1"
     http_login_password:
         description:
             - Basic Auth password
-        required: false
-        default: None
         version_added: "2.1"
     timeout:
         description:
             - The timeout of API request (seconds).
         default: 10
     validate_certs:
-      required: false
       description:
        - If set to False, SSL certificates will not be validated. This should only be used on personally controlled sites using self-signed certificates.
-      default: true
-      choices: ['true', 'false']
+      type: bool
+      default: 'yes'
       version_added: "2.5"
 '''