Add support for Strata docker_test_images

[jimmydief]

Is your feature request related to a problem? Please describe.
We set a base image for our Strata pipeline in our .strata.yml. Currently, this has to be manually updated.

Describe the solution you'd like
Ideally, this would be auto-updated as well.

Describe alternatives you've considered
Do it myself!

Additional context
Example: https://git.soma.salesforce.com/insights/pupparazzi/blob/master/.strata.yml#L11