Replace hard coded docker command to environment variable for support podman

Makefile

@@ -334,31 +334,31 @@ validate-runtime-image: # Validate that runtime image meets minimum criteria
 	echo "Validating container image $$image" ; \
 	echo "-----------------------------------------------------------" ; \
 	echo "=> Loading container image ..." ; \
-	docker inspect $$image > /dev/null 2>&1 ; \
+	$(CONTAINER_EXEC) inspect $$image > /dev/null 2>&1 ; \
 	if [ $$? -ne 0 ]; then \
 		echo Container image $$image is not present, pulling... ; \
-		docker pull $$image ; \
+		$(CONTAINER_EXEC) pull $$image ; \
 		if [ $$? -ne 0 ]; then \
 			echo "ERROR: pull of container image $$image failed" ; \
 			exit 1; \
 		fi; \
 	fi; \
 	for cmd in $$required_commands ; do \
         echo "=> Checking container image $$image for $$cmd..." ; \
-		docker run --rm --entrypoint /bin/bash $$image -c "which $$cmd" > /dev/null 2>&1 ; \
+		$(CONTAINER_EXEC) run --rm --entrypoint /bin/bash $$image -c "which $$cmd" > /dev/null 2>&1 ; \
 		if [ $$? -ne 0 ]; then \
 			echo "ERROR: Container image $$image does not meet criteria for command: $$cmd" ; \
 			fail=1; \
 			continue; \
 		fi; \
 		if [ $$cmd == "python3" ]; then \
-			IMAGE_PYTHON3_MINOR_VERSION=`docker run --rm --entrypoint /bin/bash $$image -c "$$cmd --version" | cut -d' ' -f2 | cut -d'.' -f2` ; \
+			IMAGE_PYTHON3_MINOR_VERSION=`$(CONTAINER_EXEC) run --rm --entrypoint /bin/bash $$image -c "$$cmd --version" | cut -d' ' -f2 | cut -d'.' -f2` ; \
 			if [[ $$IMAGE_PYTHON3_MINOR_VERSION -lt 8 ]]; then \
 				echo "WARNING: Container image $$image requires Python 3.8 or greater for latest generic component dependency installation" ; \
 				fail=1; \
 			elif [[ $$IMAGE_PYTHON3_MINOR_VERSION -ge 8 ]]; then \
 				echo "=> Checking notebook execution..." ; \
-				docker run -v $$(pwd)/etc/generic:/opt/elyra/ --rm --entrypoint /bin/bash $$image -c "python3 -m pip install -r /opt/elyra/requirements-elyra.txt && \
+				$(CONTAINER_EXEC) run -v $$(pwd)/etc/generic:/opt/elyra/ --rm --entrypoint /bin/bash $$image -c "python3 -m pip install -r /opt/elyra/requirements-elyra.txt && \
 							   curl https://raw.githubusercontent.com/nteract/papermill/main/papermill/tests/notebooks/simple_execute.ipynb --output simple_execute.ipynb && \
 							   python3 -m papermill simple_execute.ipynb output.ipynb > /dev/null" ; \
 				if [ $$? -ne 0 ]; then \
@@ -373,7 +373,7 @@ validate-runtime-image: # Validate that runtime image meets minimum criteria
 	done ; \
 	if [ $(REMOVE_RUNTIME_IMAGE) -eq 1 ]; then \
 		echo Removing container image $$image... ; \
-		docker rmi $$image > /dev/null ; \
+		$(CONTAINER_EXEC) rmi $$image > /dev/null ; \
 	fi; \
 	echo "-----------------------------------------------------------" ; \
 	if [ $$fail -eq 1 ]; then \

docs/source/recipes/creating-a-custom-runtime-image.md

@@ -90,6 +90,11 @@ The [Elyra `Makefile`](https://github.com/elyra-ai/elyra/blob/main/Makefile) inc
    ```bash
    $ make validate-runtime-image image=my-runtime-image
    ```
+   If using `podman`, ensure the following environmental variables are set prior to running the release script:
+```bash
+    CONTAINER_EXEC=podman
+    CONTAINER_OUTPUT_OPTION="--format docker"
+```
 
    If no problems were detected the output should look as follows: