Docs: add Mike J. as backup TW for dev guidelines

Why is this change being made?

Adds @mjang1 as backup Technical Writer for development guidelines.

gitlab-org/gitlab!30372 (merged) updates GitLab's Code Owners.

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

Related: gitlab-org/gitlab#206942 (closed)