fix: add synthetic-monitoring-dev as owners of release files (#1010)

CHANGELOG.md, package.json and
.github/release-please/release-please-config.json are updated as part of
creating a release. In order to allow anybody in the team to run that
process, add synthetic-monitoring-dev as owners of those files.

Signed-off-by: Marcelo E. Magallon <marcelo.magallon@grafana.com>

CODEOWNERS

@@ -2,3 +2,12 @@
 # https://git-scm.com/docs/gitignore#_pattern_format
 
 * @grafana/synthetic-monitoring-fe
+
+# These files are updated by release-please and we need any member of the
+# larger team to be able to approve them.
+#
+# The docs seem to suggest that the last matching pattern is the one that is
+# used, so we need to keep the * pattern above this one.
+/CHANGELOG.md @grafana/synthetic-monitoring-fe @grafana/synthetic-monitoring-dev
+/package.json @grafana/synthetic-monitoring-fe @grafana/synthetic-monitoring-dev
+/.github/release-please/release-please-config.json @grafana/synthetic-monitoring-fe @grafana/synthetic-monitoring-dev