[Community] Update Leadership Team page on Community Handbook

[RCheesley]

The following changes need to happen on the Community handbook:

Remove the following:

• Mattias Michaux
• Oluwatobi Owolabi
• Nico Grienauer

They need adding to the honor roll at the bottom of the page.

Add the following:

• Joey Keller (Product Team Lead)
• Rahul Shinde (Assistant Team Lead, Product)
• Mike Van Hemelrijck (Assistant Team Lead, Marketing)
• Avinash Dalvi (Assistant Team Lead, Community)

All email addresses are [email protected] - let me know if you have any queries.

Important note:

The current page is on the Grav website, which can be edited here: https://github.com/mautic/mautic-community-handbook/blob/main/pages/04.community-leadership/01.current-leadership-team/docs.md.

There's a project in progress to move over to Read the Docs. This page has already been ported over, so please also make the changes to this file: https://github.com/mautic/mautic-community-handbook/blob/main/docs/community_leadership/current_leadership_team.rst so that we don't lose it once we launch the new handbook!

You can make both changes in the same PR.