make sure notifiers dir exists for provisioning in docker

Dockerfile

@@ -64,6 +64,7 @@ RUN mkdir -p "$GF_PATHS_HOME/.aws" && \
     useradd -r -u $GF_UID -g grafana grafana && \
     mkdir -p "$GF_PATHS_PROVISIONING/datasources" \
              "$GF_PATHS_PROVISIONING/dashboards" \
+             "$GF_PATHS_PROVISIONING/notifiers" \
              "$GF_PATHS_LOGS" \
              "$GF_PATHS_PLUGINS" \
              "$GF_PATHS_DATA" && \

packaging/docker/Dockerfile

@@ -39,6 +39,7 @@ RUN mkdir -p "$GF_PATHS_HOME/.aws" && \
     useradd -r -u $GF_UID -g grafana grafana && \
     mkdir -p "$GF_PATHS_PROVISIONING/datasources" \
              "$GF_PATHS_PROVISIONING/dashboards" \
+             "$GF_PATHS_PROVISIONING/notifiers" \
              "$GF_PATHS_LOGS" \
              "$GF_PATHS_PLUGINS" \
              "$GF_PATHS_DATA" && \