Clients can adjust notification frequency

## Context

### Confusion about notification frequency

Raised by the Support team (Ramya) based on tickets:
> **Information about notifications for form submissions** - The Form sends a maximum of two notifications per day if the notifications turned on. The first notification is to alert the user that there is one single response waiting to be downloaded and the second notification is to alert the user that there are multiple responses waiting to be downloaded. We currently do not provide the functionality to have an email reminder sent out for every form submission.

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This could be clarified and/or retought in terms of the description and/or frequency options we provide, why does it max out at 2 per day?

We might consider a summary at the end of the day or week instead? and/or the option to send an email message for each submission individually?

https://gcdigital.slack.com/archives/C03T4FAE9FV/p1763061633825809
> Hi, I have activated the function "Receive notifications" in multiple published forms, and I do not receive a notification every time someone sends a new completed form. It only works the first two forms of the day. As I do not get notified every time a new form comes in, it’s useless to our process, as we need to know every time someone submits a completed form. It does not matter to us if we receive 100 notification per day, we NEED to know 100 forms were submitted, it’s the entire point. Thank you!

## Currently

- Get notification for first response of the day
- Get notification for next reponse of the day
- Don't get subsequent notifications that day
(max 2 notifications per day if 2+ notifications)

## Proposed options to choose from

Select frequency based on use case / need for awareness of new responses

- Get notification for each submitted response
- OR Get daily summary of all submitted responses
- OR Get weekly summary of all submitted responses
- OR Don't get any notifications

## Other related tickets

https://github.com/cds-snc/platform-forms-client/issues/6005
https://github.com/cds-snc/platform-forms-client/issues/5885
https://github.com/cds-snc/platform-forms-client/issues/5868