Keila is now available

[girish]

Keila is available as an unstable package now.

Keila is an Open-source email newsletters for creators and businesses.

Forum category for feedback is at https://forum.cloudron.io/category/211/keila
The docs are at https://docs.cloudron.io/packages/keila/
Package repo is https://git.cloudron.io/packages/keila-app

Thanks to @andreasdueren for the initial package!