Convert str to json format before evaluating length in find_image() and inspect_image().

[nishipy]

Background
During working on #563, I found some strange behaviors of podman_image.find_image() and podman_image.inspect_image().
I guess this implementation is not as expected.

Details
These functions will execute podman commands such as podman image ls <IMG_NAME> --format json and podman image inspect <IMG_NAME> --format json.
The following snippet is from find_image(), and it looks images is expected to receive a list from rc, images, err = self._run(args, ignore_errors=True) . Then its length will be evaluated.
However, I believe that currently images is str type and it is []\n if the target image doesn't exist on a server. So len(image) will be not zero, but 3 or more.

ansible-podman-collections/plugins/modules/podman_image.py

Lines 525 to 528 in d5f7655

	args = ['image', 'ls', image_name, '--format', 'json']
	rc, images, err = self._run(args, ignore_errors=True)
	if len(images) > 0:
	return json.loads(images)

I think that the expectation here is len(image) will be zero if the target image is absent.
Therefore, this PR fixes that and converts str to json format before evaluating its length in find_image() and inspect_image().

[sshnaidm]

Would be nice to add test to it.

[sshnaidm]

Thanks for fix!