Per changes requested

- build-extra-tests composite-action comment changed to Builds extra test required for FireSim tests
- removed unneeded inputs tools-version and group-key from run-tests composite action
- Added better comment to toolchain-build composite action
- Change CI_MAKE_NPROC back to 8 in defaults.sh
- Moved all the duplicated enviroment setting stuff in workflow file to the top
  - BUILDSERVER, BUILDUSER, CI_DIR, SERVER, and JVM_OPTS
- Romoved all the not needed passed parameters in the calls to run-script
- A bit of cleanup to .github/README.md
  - added link to SO `if` hack
  - cleaned up comments on CI_DIR
  - removed bad empty final bullet line

.github/scripts/defaults.sh

@@ -18,7 +18,7 @@ clean () {
 }
 
 # make parallelism
-CI_MAKE_NPROC=4
+CI_MAKE_NPROC=8
 # chosen based on a 24c system shared with 1 other project
 REMOTE_MAKE_NPROC=4