On PR, only build samples that have changed

[bart-vmware]

Given the current resource constraints on dhaka, we should only build samples that have changed.

This can be done using Use Azure DevOps path expressions, such as in https://github.com/SteeltoeOSS/Steeltoe/blob/main/build/connectors.yml.

In order to test, we need two PRs. The first one changes the yaml files (which would trigger a rebuild of all tests). The second PR (based on the first one, and targeting the branch of the first PR) only touches files within the Management sample. The second PR should run only the tests for management.