Better make it clearer under each section what the labels are
rather than listing a subset of them in the section title

A section was moved in f644b8c8 but this got lost.

As discussed in https://gitlab.com/gitlab-org/gitlab-ce/issues/42891

- Clearly define new priority issue for bugs
- Clarrified existing priority label => Milestone labels

The bug guidelines example of what should be marked with the stewardship
label goes against the principles of GitLab as stated in
https://about.gitlab.com/stewardship/ since mentions removing a feature
from GitLab CE to make it exclusive of GitLab EE.

The example should be the opposite, where GitLab Inc. is bringing a
feature from GitLab EE to GitLab CE.

This commit changes the example to reflect this situation.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/43579