[tc][all][senlin] Retiring the Senlin project

Hello everyone,

As you might know, the Senlin project is not active and was marked 'inactive' since 2024.1 cycle[1]. In this cycle also, this project is leaderless[2] and no maintainer stepped up to maintain it. As discussed in the Leaderless project etherpad[2], the next step is to retire the project.

I'm sending this email to propose the Senlin retirement and based on the response, I will proceed next.

[1] https://governance.openstack.org/tc/reference/emerging-technology-and-inacti... [2] https://etherpad.opendev.org/p/2024.2-leaderless#L72

-gmann