UI improvements for custom workflows on free plan

[CarinaWolli]

Context: On a free plan, users can only use our predefined templates.

1. Custom should be disabled in the dropdown and have an Upgrade badge the redirects to /teams

2. Add variable dropdown should also be disabled

[linear]

CAL-7109

[Ashutosh0x]

Hi @CarinaWolli, I've implemented the UI improvements for the free plan in PR #27077.

These changes:

• Restricted custom email editing to paid plans (\hasPaidPlan).
• Hid the 'Add variable' dropdown for free users on email actions.
• Fixed the issue where paid users were seeing a disabled editor by mistake.

Ready for review!