Introduce MONAI_PY_EXE env var for run script

With this patch, we can use different python3 binary
by exporting MONAI_PY_EXE env variable.

By default, it is set to 'python3'

Author: gigony

run

@@ -20,6 +20,8 @@ init_globals() {
     fi
 
     export TOP=$(git rev-parse --show-toplevel || $(dirname "${RUN_SCRIPT_FILE}"))
+    MONAI_PY_EXE=${MONAI_PY_EXE:-"python3"}
+    export MONAI_PY_EXE
 }
 
 ################################################################################
@@ -283,7 +285,7 @@ get_package_info() {
 
     [ -z "${app_path}" ] && c_echo_err R "No application path specified." && return 1
 
-    python3 $TOP/monai/deploy/utils/importutil.py get_package_info ${app_path} ${model_path}
+    ${MONAI_PY_EXE} $TOP/monai/deploy/utils/importutil.py get_package_info ${app_path} ${model_path}
 }
 
 #==================================================================================
@@ -292,15 +294,15 @@ get_package_info() {
 
 install_python_dev_deps_() {
     if [ -n "${VIRTUAL_ENV}" ] || [ -n "${CONDA_PREFIX}" ]; then
-        run_command python3 -m pip install -q -U setuptools pip wheel
-        run_command python3 -m pip install -q -r ${TOP}/requirements-dev.txt
-        run_command python3 -m pip install -q -r ${TOP}/requirements-examples.txt
+        run_command ${MONAI_PY_EXE} -m pip install -q -U setuptools pip wheel
+        run_command ${MONAI_PY_EXE} -m pip install -q -r ${TOP}/requirements-dev.txt
+        run_command ${MONAI_PY_EXE} -m pip install -q -r ${TOP}/requirements-examples.txt
 
     else
         c_echo_err R "You must be in a virtual environment to install dependencies."
         if [ ! -e "$TOP/.venv/dev/bin/python3" ]; then
             c_echo_err W "Installing a virtual environment at " G "$TOP/.venv/dev" W " ..."
-            run_command python3 -m venv "$TOP/.venv/dev"
+            run_command ${MONAI_PY_EXE} -m venv "$TOP/.venv/dev"
         fi
 
         c_echo_err W "Please activate the virtual environment at " G "$TOP/.venv/dev" W " and execute the setup command again."
@@ -314,10 +316,10 @@ install_python_dev_deps_() {
     # This solves an issue with separate package folders for 'monai' and 'monai-app-sdk' like below:
     # - 'monai': installed with 'pip install monai'
     # - 'monai-app-sdk': installed with 'pip install -e .  # installed with development(edit) mode
-    local monai_package_path=$(python3 $TOP/monai/deploy/utils/importutil.py dist_module_path monai)
-    local sdk_package_path=$(python3 $TOP/monai/deploy/utils/importutil.py dist_module_path monai-app-sdk)
+    local monai_package_path=$(${MONAI_PY_EXE} $TOP/monai/deploy/utils/importutil.py dist_module_path monai)
+    local sdk_package_path=$(${MONAI_PY_EXE} $TOP/monai/deploy/utils/importutil.py dist_module_path monai-app-sdk)
     local is_sdk_editable="false"
-    if python3 $TOP/monai/deploy/utils/importutil.py is_dist_editable monai-app-sdk; then
+    if ${MONAI_PY_EXE} $TOP/monai/deploy/utils/importutil.py is_dist_editable monai-app-sdk; then
         is_sdk_editable="true"
     fi
 
@@ -328,16 +330,16 @@ install_python_dev_deps_() {
     if [ "${is_sdk_editable}" == "false" ]; then
         c_echo W "Installing monai-app-sdk in edit mode..."
         if [ -n "${VIRTUAL_ENV}" ] || [ -n "${CONDA_PREFIX}" ]; then
-            run_command python3 -m pip install -e .
+            run_command ${MONAI_PY_EXE} -m pip install -e .
         else
             c_echo_err R "You must be in a virtual environment to install monai-app-sdk in edit mode."
         fi
 
-        if python3 $TOP/monai/deploy/utils/importutil.py is_dist_editable monai-app-sdk; then
+        if ${MONAI_PY_EXE} $TOP/monai/deploy/utils/importutil.py is_dist_editable monai-app-sdk; then
             is_sdk_editable="true"
         fi
 
-        sdk_package_path=$(python3 $TOP/monai/deploy/utils/importutil.py dist_module_path monai-app-sdk)
+        sdk_package_path=$(${MONAI_PY_EXE} $TOP/monai/deploy/utils/importutil.py dist_module_path monai-app-sdk)
         c_echo b "sdk_package_path  : " Z "${sdk_package_path}"
         c_echo b "is_sdk_editable   : " Z "${is_sdk_editable}"
     fi