Improve ecloud invitation format

Summary

Improve the copy for meeting invites sent by ecloud. Build on top of issue https://gitlab.e.foundation/e/backlog/-/issues/4264

Description

What is the current behavior?

Meeting invite copy is very limited and contains only the name of the organizer, the title, the time and the localization.

What is the improved behavior?

In the body of the invite email add the description of the event and the list of participants.

And in the to field of the invite email addr the name/email address of the other invitees, in cc field the name/email address of the optional invitees.

What does it bring?

More clarity on the meeting owner, the meeting attendees and the meeting details

Examples

Ecloud	Gmail	Fastmail

Validation