changelog update

Author: rcaril

CHANGELOG.md

@@ -15,6 +15,7 @@
 - feat(service/version): Add 'service version ...' commands as replacements for 'service-version ...', with unlisted and deprecated aliases of 'service-version ...'. ([#1614](https://github.com/fastly/cli/pull/1614))
 - feat(service/vcl): moved the `vcl` command under the `service` command, with an unlisted and deprecated alias of `vcl` ([#1616](https://github.com/fastly/cli/pull/1616))
 - feat(service/healthcheck): moved the `healthcheck` command under the `service` command, with an unlisted and deprecated alias of `healthcheck` ([#1619](https://github.com/fastly/cli/pull/1619))
+- feat(service/healthcheck): moved the `backend` command under the `service` command, with an unlisted and deprecated alias of `backend` ([#1621](https://github.com/fastly/cli/pull/1621))
 
 ### Bug fixes: