* Adding missing return statement to FormPage.process_form_submission in the "Custom form submission model" example to make it available to FormPage.render_landing_page, among other methods.
- apply general fixes to existing markdown documentation
- various cases of rst syntax still used
- update some links to be the new format
- clean up line breaks (prettier)
- the original conversion to markdown happened around the same time as the MyST conversion
- this meant that the syntax was not in sync
- also run prettier over markdown for consistent formatting & whitespace
- see #8007