Correct the name of matrix-bot-baibot's configuration file

[hardye]

Commit 30dad8b renamed the config file for baibot from config.yml to config.yaml. While this increases consistency, it actually broke my baibot setup: the service matrix-bot-baitbot.service failed to start because the baibot container apparently expects the file's name to be config.yml (without the 'a').

This PR reverts part of the changes introduced in 30dad8b to ensure the container gets the file name it expects.

[spantaleev]

Thanks for reporting this and working on a fix! 🙇