Add Alina Mihaila as reviewer and trainee_maintainer of GitLab and trainee_maintainer of version-gitlab-com

Why is this change being made?

In order to become a reviewer

Description

Add Alina Mihaila as:

• code reviewer for GitLab
• Trainee BE maintainer GitLab
• Trainee BE maintainer version-gitlab-com

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

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