NEXT-00000 - Activate headless sales channel without a theme

[sobyte]

1. Why is this change necessary?

See #3474

2. What does this change do, exactly?

Add condition to activation toggle to exclude headless sales channels.

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

See #3474

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

#3474

5. Checklist

• I have rebased my changes to remove merge conflicts
• I have written tests and verified that they fail without my change
• I have created a changelog file with all necessary information about my changes
• I have written or adjusted the documentation according to my changes
• This change has comments for package types, values, functions, and non-obvious lines of code
• I have read the contribution requirements and fulfil them.

[CLAassistant]

All committers have signed the CLA.

[marcelbrode]

LGTM 👍

@sobyte Would you mind adding a jest test case for that? 😄

[marcelbrode]

Hi there. 2 Weeks have passed, anything new here? 🙂