Updated and standardised commit messages

Why is this change being made?

When committing to a gitlab-org project, the following enforcement checks are made on commit messages:

• Message begins with a capital letter
• Message does not end with a period (.)

General MR Guidelines

This MR brings the commit messages given to students following the GitLab Certification paths (hands on labs) in line with the same guidelines, in order to teach newcomers habits they should maintain.

I also standardised a couple of references from "Commit message box" to "Commit message field"

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this MR to the correct Directly Responsible Individual/s (DRI)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the Maintained by section on the page being edited
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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