Make internal licensing section more discoverable in search

Why is this change being made?

A few minutes ago, I struggled to find information in the handbook about generating developer licenses. I was searching for keywords like "developer license", "internal license", "team member license", etc. There were no results. I ended up asking in Slack#g_license, and @jameslopez immediately gave me the answer: Working on GitLab EE.

I am unlikely to be the only person searching for this content using those keywords. Also, this section of the handbook is focused on licenses. So this MR expands that section title to use some of those license-related keywords to improve searchability.

Author Checklist

• Provided a concise title for the 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 change to the correct DRI(s)
  • 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 in 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.

---