Update Web IDE for GitLab 16 in practical handbook edits

Why is this change being made?

The Web IDE based on VS Code will become the new default with GitLab 16.0 on 2023-05-22, GitLab.com SaaS is already updated. This MR revises the practical handbook editing handbook introduction, and adds more URLs into the GitLab documentation to avoid duplicating information.

It also updates missing features that have been added to the workflows since January 2023.

All information to use the Web IDE is still accurate, and do not require new images/videos at this point.

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, and the content is SAFE
• 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
  • The when to get approval handbook section explains the workflow in more detail
• 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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