Add support for MailJet Webhooks and Emails

[tsutomi]

The Deveel.Webhooks project currently does not support MailJet webhooks and emails. This issue is to add support for MailJet so that users of the project can receive and process incoming webhooks and emails from that provider in ASP.NET Core applications.

Tasks

• Implement a new package Deveel.Webhooks.Receiver.MailJet with middleware components to handle incoming webhooks and emails from MailJet.
• Write a parser for MailJet webhook events and a handler to process them. See the MailJet documentation on webhooks for more information on the event format.
• Write a parser for MailJet email events and a handler to process them. See the MailJet documentation on emails for more information on the email event format.
• Update the documentation to include examples and instructions for how to use the new MailJet package.

Expected Outcome
The Deveel.Webhooks project will have support for MailJet webhooks and emails, allowing users to receive and process incoming webhooks and emails from MailJet using the new Deveel.Webhooks.Receiver.MailJet package.

** Difficulty** - Easy