add git.tag to get the tag on a certain commit

[blackwhale]

Context

${git.tags} returns all the tags contains the current commit and ${git.closest.tag.name} could return the tag name not belonging to the commit. A new property is added in this PR, ${git.tag}, which returns the tag(s) of a certain commit and empty string if the commit doesn't has a tag.

Contributor Checklist

• [v] Added relevant integration or unit tests to verify the changes
• [v] Update the Readme or any other documentation (including relevant Javadoc)
• [v] Ensured that tests pass locally: mvn clean package
• [v] Ensured that the code meets the current checkstyle coding style definition: mvn clean verify -Pcheckstyle -Dmaven.test.skip=true -B

[TheSnoozer]

Hello, thanks for your contribution! LGTM.