Fix docker image tag in release template (#9425)

**What this PR does / why we need it**:
Releases in GitHub are published automatically from Drone. Drone calls
the `tools/release` script which uses the `tools/release-note.md`
template to generate the release body.

Before this PR, the template used the `$DRONE_TAG` env variable which
had a `v` preffix (e. `v2.8.0`). Since we publish the docker images
without the `v` preffix, the docker images referenced by the release did
not exist. This affected the `v2.8.0`, `v2.8.1` and `v2.8.2` releases.

I manually fixed the `v2.8.0`, `v2.8.1` and `v2.8.2` release pages, but
this PR should fix the template so we no longer run into this situation.

**Which issue(s) this PR fixes**:
Fixes https://github.com/grafana/loki/issues/9384

**Special notes for your reviewer**:

Not sure where to find the available env variables in Drone. I wonder if
there is an existing env var with the version without the `v` preffix.

**Checklist**
- [ ] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)
- [ ] Documentation added
- [ ] Tests updated
- [ ] `CHANGELOG.md` updated
- [ ] Changes that require user attention or interaction to upgrade are
documented in `docs/sources/upgrading/_index.md`

tools/release

@@ -1,4 +1,7 @@
 #!/usr/bin/env bash
+DRONE_TAG_NO_V=${DRONE_TAG#v}
+export DRONE_TAG_NO_V
+
 ghr \
   -t "${GITHUB_TOKEN}" \
   -u "${DRONE_REPO_OWNER}" \

tools/release-note.md

@@ -11,8 +11,8 @@ The components of Loki are currently distributed in plain binary form and as Doc
 * https://hub.docker.com/r/grafana/loki
 * https://hub.docker.com/r/grafana/promtail
 ```bash
-$ docker pull "grafana/loki:${DRONE_TAG}"
-$ docker pull "grafana/promtail:${DRONE_TAG}"
+$ docker pull "grafana/loki:${DRONE_TAG_NO_V}"
+$ docker pull "grafana/promtail:${DRONE_TAG_NO_V}"
 ```
 
 #### Binary