Find replacement for typo3-announce

We will replace Mailman with a new tool at https://talk.typo3.org/.

It is not possible to operate 1:m communication like used for typo3-announce with this solution. Therefore, we need to look out for a new tool:

• Mailtrain - https://mailtrain.org/
• Check if we can use a hosted solution such as Mailchimp or Hubspot

INFO: The TYPO3 Association is in a very similar situation while it needs to replace the Sympa list t3a-members with something new. See #37 (closed).

Tasks

• Get in touch with Team leaders of CMS and Security team (they are currently using typo3-announce)
• Define requirements
• Decide for a tool
• Migration