Add custom metadata to the tag when releasing

[jgrodziski]

When invoking the release task, metav add some metadata as an annotation to the tag (e.g.: {"module-name":"mysys-backend","version":"0.60.1","tag":"diffusion-import-0.60.1","generated-at":"2021-09-29T15:35:50Z","path":"mysys\/backend\/"}). Metav should allow the user to add some custom metadata in addition to the built-in ones. The use case is to be able to retrieve these added metadata in the CI/CD pipeline that would be triggered by the tag and to alter the pipeline in some way. A use case would be to flag a release to be automatically deployed to production and to have others release not deployed because of more complex things to do, some manually, along the deployment (re-indexing, schema migration ,etc.).