Add jjackson as trainee maintainer on versions application.

Why is this change being made?

I would like to learn more about how this team manages and implements features on this application. There's a lot of similarities between some of our services projects and so having more insight into how they overlap will help me learn more about the different maintainers, and help identify areas in which we can collaborate and share efforts between teams.

Does this MR meet the acceptance criteria?

Being involved in more MR reviews will help with this, yes.

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what