40686 - Payment method "Free" is now assigned to an availability rule by default

1. Why is this change necessary?

It's a bug fix.

2. What does this change do, exactly?

It creates and assigns an availability rule to the payment method.

3. Describe each step to reproduce the issue or behavior.

1. Install or update & activate the plugin
2. Ensure the payment method "Free" is assigned to the sales channel
3. Ensure the payment method "Free" is only available in the storefront as the rule is configured

4. Please link to the relevant issues (if any).

https://redmine.netinventors.de/issues/40686

5. Checklist

• I have updated the plugin version and changelog
• I can confirm the code style fits our requirements
• I can confirm that no debug output is generated anywhere
• I have changed the required NetiFoundation-version to the latest available version

6. Release Notes