Changed Docker image tagging to use semver tags for releases. (#10648)
* Changed Docker image tagging to use semver tags for releases. This allows users to use image names like `netdata/netdata:1` or `netdata/netdata@1.29` and track the most up-to-date release that matches that version prefix. Such usage is a common practice for projects using semantic versioning like we are. This has a side effect, however, of remivng the `v` from the start of our version tags. Not having it is also more consistent with how a vast majority of other projects handle version tags, but users will need to be notified about the change. * Proper backwards compatability. * Add documentation about Docker image tags. * Update packaging/docker/README.md Co-authored-by: Joel Hans <joel.g.hans@gmail.com> Co-authored-by: Joel Hans <joel.g.hans@gmail.com>