Provide clarity on breaking changes decision

Why is this change being made?

Closes Product#4491 (closed)

This MR adds additional clarity to our definition of a breaking change by:

• simplifying the opening paragraph into a few bullet points
• providing 3 yes or no questions to help the contributor determine if the change is a breaking change
• providing an example for each of the 3 yes or no questions for additional guidance

This MR also replaces "customers" with "users" and makes some minor revisions to verbiage and grammar.

Is this a breaking change?

If the answer is yes to any of the following questions, the change is to be considered a breaking change and should only be introduced in a major version.

• Does this change require an action from the customer to ensure continuity of function?
• Does this change cause a disruption to a customer's workflows or tasks?
• Does this change cause other parts of the product to fail?

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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