Update dockerfile in aries-cloudagent-container to be based on Python 3.9 instead of 3.6

[swcurran]

Update the dockerfile as needed to enable publishing the image to the bcgovimages organization in the Docker Hub container registry.

As I recall, all we need to do is pull the image from the GitHub Container Registry and publish it, so that it continues to be available in both places.

[swcurran]

Completed.