Use Release notes as Tag annotation

[hutson]

Modify conventional-gitlab-releaser to assign the changelog/release notes to the message property so that the release notes are used as the tag annotation.

There's some interest within the GitLab community to store the changelog/release notes in the tag annotation - https://gitlab.com/gitlab-org/gitlab-ce/issues/20587

Code to change - https://github.com/conventional-changelog/releaser-tools/blob/8687ae4cf4650c2ab10e73ede0ef785fe816e98a/packages/conventional-gitlab-releaser/src/index.js#L82