add collective.mastodon

[MrTango]

I already added the addon and deployed on testing, but i don't really know where to set the environment variables in this stack. May @fredvd or @davisagli can help me out here?

[davisagli]

@MrTango Environment variables for the Zope instances can be added here: https://github.com/plone/tagung.plone.de/blob/main/devops/stacks/tagung.plone.de.yml#L44

If it is a something sensitive like an API token, that should reference a Docker secret (https://docs.docker.com/compose/how-tos/use-secrets/) which we add on the Docker swarm.