Fixes Isaac Sim executable on pip installation (#1172)

# Description

This PR fix https://github.com/isaac-sim/IsaacLab/issues/831 by taking
into account the Isaac Sim installation using PIP

- Bug fix (non-breaking change which fixes an issue)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

isaaclab.bat

@@ -81,7 +81,7 @@ if errorlevel 1 (
     set isaacsim_exe=!isaac_path!\isaac-sim.bat
 ) else (
     rem if isaac sim installed from pip
-    set isaacsim_exe=isaacsim
+    set isaacsim_exe=isaacsim omni.isaac.sim
 )
 rem check if there is a python path available
 if not exist "%isaacsim_exe%" (

isaaclab.sh

@@ -90,8 +90,14 @@ extract_isaacsim_exe() {
     local isaacsim_exe=${isaac_path}/isaac-sim.sh
     # check if there is a python path available
     if [ ! -f "${isaacsim_exe}" ]; then
-        echo "[ERROR] No Isaac Sim executable found at path: ${isaacsim_exe}" >&2
-        exit 1
+        # check for installation using Isaac Sim pip
+        if [ $(python -m pip list | grep -c 'isaacsim-rl') -gt 0 ]; then
+            # Isaac Sim - Python packages entry point
+            local isaacsim_exe="isaacsim omni.isaac.sim"
+        else
+            echo "[ERROR] No Isaac Sim executable found at path: ${isaac_path}" >&2
+            exit 1
+        fi
     fi
     # return the result
     echo ${isaacsim_exe}