Add team focus for Andreas and Greg

Per https://gitlab.com/gitlab-com/infrastructure/issues/3918 and https://gitlab.com/gitlab-com/infrastructure/issues/3139 database engineers will focus on the work/problems of specific functional groups (but not report to those groups).

I have left myself out for the time being as I am still involved in too many different teams/tasks. Once we have a DB manager and an additional engineer I will hopefully be able to focus on a specific functional group as well.

Fixes https://gitlab.com/gitlab-com/infrastructure/issues/3918

@abrandl @_stark Any objections against these assignments?