SE-2649 Deep link to reference materials

Updates handbook content to allow for deep-linking from the onboarding course.

Also adds some deep links to critical roles and terms to the handbook, adds requirement to document incidents to the firefighter role, and fixes some formatting.

Testing instructions

• Read the updated glossary page. Check for accuracy and note that the headers added for each term created anchors.
• Check these changes made to the roles page for clarity and correct links:
  • link to "sprint firefighter" or "firefighter" go to the glossary firefighter entry.
  • newcomer role links added for the task reviewer, mentor, and firefighter go to the correct glossary entries.
  • firefighter role bullet point added to describe the newly-added requirement to document incidents.
• Formatting typos fixed on:
  • List spacing re-added for the Newcomer > Onboarding Epic Ownership section (cf forum comment).
  • Sprint planning > Grooming "planning session"

Reviewer

• @guruprasad