Support updating `image_tag` in Strata infra templates for externally hosted service images

[doshitan]

Context

With more robust support in the Strata infra templates for running arbitrary container images, we should provide a way to automatically update those image configurations inside infra templates.

Implementation

Likely via the regex manager: https://docs.renovatebot.com/modules/manager/regex/

Similar to how the upstream customManagers:dockerfileVersions works: https://docs.renovatebot.com/presets-customManagers/#custommanagersdockerfileversions