Streamline integrations.toml author vs maintainer

We seem to mix author and maintainer in the projects in the integrations.toml. We probably want to clean this up a bit.

Possible solutions:

- Use only one of them
- Use author for the original author and maintainer for when someone takes over a project to maintain it.

Start by reviewing integrations.toml and comparing how author and maintainer are used across its project entries. Determine which ownership rule the project wants, then normalize the affected entries and verify that each project consistently uses the chosen fields.

Written by the indexing model from the issue text.