Fix SES error preventing email to >50 recipients

[dunkOnIT]

The following error was triggered when results for FMC 2024 were submitted - a competition with >50 delegates.
Net::SMTPFatalError (554 Transaction failed: Recipient count exceeds 50.

The following fixes should be implemented:

• Short-term: Add a validation for when there are >=50 organizers/delegates on a competition (not sure if we need to check for delegates AND organizers, or just delegates)
• Long-term: Do whatever we need to do to be able to send to >= 50 recipients

[gregorbg]

As per https://docs.aws.amazon.com/ses/latest/dg/quotas.html, adding more than 50 recipients is really not an option for AWS. We should probably implement a hard validation for this edge case in our own WCA code.

[FinnIckler]

It also says that the best solution is just to send individual emails.

"Defining multiple recipients in a message destination can lead to poor observability as well as poor deliverability and should not be used unless your use case specifically requires it."

But they probably also have some bias i.e costs :P