Confirm before emailing all contributors in Gitcoin grants campaigns

### User Story

[comment]: As someone running a Gitcoin Grant campaign, I want a confirmation step when I submit a post that will be emailed to all of my contributors, so I don't spam them with incomplete/improperly formatted emails if I accidentally hit [ENTER] while typing an update.

### Why Is this Needed

[comment]: # Currently, it is really easy to accidentally post a message if you try to create a new line. [shift] + [enter] gives makes a new line, while [enter] posts the message.

This behaviour is fine when posting to the feed, because you can simply edit or delete the post if it is incorrect.

However, when you have selected the checkbox to email the message out to all of your contributors, mistakenly hitting the [enter] key sends the incomplete message out as an email, which cannot be undone.

A confirmation step, or removing the post on [enter] function while the checkbox is TRUE, would mostly alleviate this issue.

*Summary*:

### Description

[comment]: # (Feature or Bug? i.e Type: Bug)
*Type*: Bug

### Current Behavior
[comment]: No confirmation step when email checkbox is TRUE

### Expected Behavior
[comment]: # Confirmation step or no send on [enter]