Add job to build the base-python3.10 image

What does this MR do?

Build and publish the base-python3.10 image via the pipeline when:

• The dockerfile has changed and we are a scheduled pipeline
• The dockerfile has changed and we are on the default branch
• The BUILD_PYTHON3_10 runtime pipeline variable is set

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab/-/issues/409140+

GitLab Docs MR