Update xr commands help layout

[sverdlov93]

• The pull request is targeting the dev branch.
• The code has been validated to compile successfully by running go vet ./....
• The code has been formatted properly using go fmt ./....
• All static analysis checks passed.
• All tests have passed. If this feature is not already covered by the tests, new tests have been added.
• All changes are detailed at the description. if not already covered at JFrog Documentation, new documentation have been added.

---

following jfrog/jfrog-cli#2539

move jf xr under command namespaces