Made docker tag configurable

Makefile

@@ -43,7 +43,7 @@ deb-rere: deb-rebuild deb-reinstall ## Rebuild and reinstall deb package
 
 docker: ## Build Docker image
 	$(MCIS) $(POM) -am -pl :rdf-processing-toolkit-pkg-docker-cli $(ARGS)
-	cd rdf-processing-toolkit-pkg-parent/rdf-processing-toolkit-pkg-docker-cli && $(MS) jib:dockerBuild && cd ../..
+	cd rdf-processing-toolkit-pkg-parent/rdf-processing-toolkit-pkg-docker-cli && $(MS) $(ARGS) jib:dockerBuild && cd ../..
 
 release-bundle: ## Create files for Github upload
 	@set -eu

README.md

@@ -111,6 +111,17 @@ make release-bundle      # Create files for Github upload
 
 A docker image is available at https://registry.hub.docker.com/r/aksw/rpt
 
+The docker image can be built with a custom tag by setting the property `docker.tag`.
+The default for `docker.tag` is `${docker.tag.prefix}${project.version}`, where `docker.tag.prefix` defaults to the empty string.
+When only setting `docker.tag.prefix` to e.g. `myfork-` then the tag will have the form `myfork-1.2.3-SNAPSHOT`.
+
+```bash
+make docker
+
+# Example for providing a custom docker tag via make:
+make docker ARGS='-D"docker.tag.prefix=experimental-"'
+```
+
 ## License
 The source code of this repo is published under the [Apache License Version 2.0](LICENSE).
 Dependencies may be licensed under different terms. When in doubt please refer to the licenses of the dependencies declared in the `pom.xml` files.

rdf-processing-toolkit-pkg-parent/rdf-processing-toolkit-pkg-docker-cli/pom.xml

@@ -15,6 +15,9 @@
 		<!-- <deb.jarFile>${project.artifactId}-${project.version}.jar</deb.jarFile> -->
 		<!-- <deb.jarFile>${project.artifactId}-${project.version}-jar-with-dependencies.jar</deb.jarFile> -->
 		<deb.jarFile>${project.artifactId}-${project.version}.jar</deb.jarFile>
+
+		<docker.tag.prefix></docker.tag.prefix>
+		<docker.tag>${docker.tag.prefix}${project.version}</docker.tag>
 	</properties>
 	<build>
 		<plugins>
@@ -40,8 +43,8 @@
 						<!-- <image>docker.io/aklakan/rdf-processing-toolkit</image> -->
 						<image>docker.io/aksw/rpt</image>
 						<tags>
-							<tag>${project.version}</tag>
-							<tag>latest</tag>
+							<tag>${docker.tag}</tag>
+							<!-- <tag>latest</tag> -->
 						</tags>
 					</to>
 					<from>