doc: make root markdown files uppercase
Most the .md files in the root of the repo are uppercase, so this PR updates glossary.md and onboarding.md to be the same.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Most the .md files in the root of the repo are uppercase, so this PR updates glossary.md and onboarding.md to be the same.