feat: add option to provide cancellation reason for email

[nrademacher]

What does this PR do?

Closes #1451 by adding an option to provide a reason when cancelling event, which is added to the cancellation email.

Type of change

• New feature (non-breaking change which adds functionality)

How should this be tested?

• Verified the new field is present by logging the email markup that would be sent to the cancelling attendee or organiser

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code and corrected any misspellings
• I have commented my code, particularly in hard-to-understand areas
  • Not warranted
• I have made corresponding changes to the documentation
  • Not applicable
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
  • This would involve creating a functionality mocking setup; would skip if possible, considering the scope of the change
• New and existing unit tests pass locally with my changes

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[zomars]

Can we hide the field when the reason is empty, or add a "No reason provided" message?

[nrademacher]

Can we hide the field when the reason is empty, or add a "No reason provided" message?

You're right, blank field looks odd. In case there's no reason given, it would in my opinion be best to omit the field in the email.

[zomars]

You're right, blank field looks odd. In case there's no reason given, it would in my opinion be best to omit the field in the email.

Agreed!

[alishaz-polymath]

I think this might a good PR to add Rejection reason as well. Thoughts @zomars, @emrysal ?

[zomars]

I think this might a good PR to add Rejection reason as well. Thoughts @zomars, @emrysal ?

We could follow up in another PR 👍🏽

[zomars]

I'll merge once checks pass. Thank you for contributing! 🙏🏽