Adds v-pre to code blocks in comments

## What does this MR do?

Allows users to comment on discussions with code that contains `{{`

Previously because of the discussion part being a Vue app it was being converted by Vue & therefore creating JS errors & the code not displaying correctly. This adds `v-pre` onto the code element to allow the user to write code that would contain `{{`

## What are the relevant issue numbers?

Closes #22911

See merge request !6674