CI(Docker): Configure renovate updates for PDAL in Dockerfiles (#3810)

* CI(renovate): Enable dockerfile version comment upgrades
* CI(docker): Configure Renovate updates for PDAL in Dockerfiles

Author: echoix

renovate.json5

@@ -9,6 +9,10 @@
         // "# renovate: " to update _VERSION 
         // environment variables in GitHub Action files.
         "customManagers:githubActionsVersions",
+        // allows to use comments starting with
+        // "# renovate: " to update _VERSION
+        // ENV or ARG in a Dockerfile.
+        "customManagers:dockerfileVersions",
 
         // when a dependency is really out of date, this will prevent to skip directly to the latest version.
         ":separateMultipleMajorReleases",