docs: Standardize "Note" blockquote usage (#11724)

Standardize the blockquote "Notes" usage, so all places are using the
`>` blockquote notation, as well as a consistent style for the "Note"
word.

PS: Thought that bolding the word "**Note**" would make for a higher
visual distinction, so went for it in all existing cases! No strong
feelings, though; happy to roll back to just "Note:" if that's
preferrable!

Release Notes:

- N/A