feature: implement endpoint for sending verification emails

[Isak-Bego]

Brief description:

We aim to provide our users with the functionality of being able to retry sending a verification email if they don't receive it. This way the process of verifying is safer.

For this reason, we have to have an endpoint that the client side can trigger by passing the email or participant object id that will retry sending a verification email. This endpoint can be an extension of the already established verification endpoint /api/v3/hackathon/participants/verify. A suggestion could be /api/v3/hackathon/participants/verify/send-email

How to achieve it:

We should rate limit this process in case someone tries to spam the endpoint and rate limit our resend service (since with the free tier we can only send so many emails within a given time). @cl3vy has already provided a working solution. We firstly need to update the structure of the participant document to:

@dataclass(kw_only=True)
class Participant(Base):
    """A representation of the Participant entity in Mongo. It is also the schema of how the entity should look
    like in Mongo before it is inserted"""
    name: str
    email: EmailStr
    is_admin: bool
    email_verified: bool = field(default=False)
    team_id: Optional[SerializableObjectId]
    last_sent_email: Optional[datetime] = field(default=None)

Then every time we get a request in this endpoint, we check if enough time has passed since the last email sent.

        # Check rate limit
        if participant.last_sent_email:
            if datetime.now() - participant.last_sent_email < timedelta(seconds=RATE_LIMIT_SECONDS):
                LOG.error(f"Rate limit exceeded for participant {participant.id} with email {participant.email}.")
                return Err(EmailRateLimitExceededError())

If the rate limit is not exceeded you proceed with sending the email.
You can get some inspiration from these changes: 600e52d

Prerequisites

The following issues should be closed before starting work with this one:

• feature: implement the verification of admin participant #807
• feature: implement the verification of random participant #808
• feature: add resend for sending emails #744