dev/event#6 Follow the 'same email' participants config setting for backend participants

[mlutfy]

https://lab.civicrm.org/dev/event/issues/6

Overview

We have the following use-case:

• Organisation using CiviEvent for a box office, i.e. to sell tickets for concerts
• People may buy multiple tickets for concerts, and often not at the same time.

For example, they may have bought a ticket during pre-sales, then later bought a ticket as a gift for a friend.

The front-end allows this, thanks for the "allow same participant emails". However the backend does not validate this option. When adding a backend registration, if the participant has already bought a ticket, the admin will get an error message: "This contact has already been assigned to this event."

Looking at Stack Exchange, I found this thread:
https://civicrm.stackexchange.com/questions/15826/enable-multiple-event-registration-for-same-purchaser-participant

Before

Cannot register a contact more than once to the same event.

After

Allow to register.

Technical Details

Needs a test? Also may need a documentation update.

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[eileenmcnaughton]

This is just loosening a form rule in a way that makes sense - I feel pretty comfortable with it. If it were post submit I'd be wanting a test