docs: Document QUARTO_PROJECT_SCRIPT_PROGRESS and QUARTO_PROJECT_SCRIPT_QUIET env vars (#1894)

* Document QUARTO_PROJECT_SCRIPT_PROGRESS and QUARTO_PROJECT_SCRIPT_QUIET env vars

Add two new environment variables from quarto-dev/quarto-cli#12444 to the
pre/post render scripts documentation and the environment variables reference.
These let scripts adapt their output based on progress display availability
and quiet mode.

* Fix markdown tables

Author: cderv