DM-48382: sasquatch app metrics - use nightly telegraf

[telegraf](https://github.com/influxdata/telegraf) has still not released the [feature to allow union fields to be specified as tags](influxdata/telegraf@bcea9a2), which will let us get a `service` tag on some Gafaelfawr metrics.
This is planned to be released in [v1.34.0](https://github.com/influxdata/telegraf/milestone/118).
Until then, we'll use a nightly telegraf build from 2025-01-09 and pushed to our `lsst-sqre` github docker registry (ghcr.io):

```
docker pull quay.io/influxdb/telegraf-nightly:alpine
docker tag quay.io/influxdb/telegraf-nightly:alpine ghcr.io/lsst-sqre/telegraf:nightly-alpine-2025-01-09
docker push ghcr.io/lsst-sqre/telegraf:nightly-alpine-2025-01-09
```

applications/sasquatch/README.md

@@ -97,8 +97,8 @@ Rubin Observatory's telemetry service
 | app-metrics.globalAppConfig | object | See `values.yaml` | app-metrics configuration in any environment in which the subchart is enabled. This should stay globally specified here, and it shouldn't be overridden.  See [here](https://sasquatch.lsst.io/user-guide/app-metrics.html#configuration) for the structure of this value. |
 | app-metrics.globalInfluxTags | list | `["application"]` | Keys in an every event sent by any app that should be recorded in InfluxDB as "tags" (vs. "fields"). These will be concatenated with the `influxTags` from `globalAppConfig` |
 | app-metrics.image.pullPolicy | string | `"Always"` | Image pull policy |
-| app-metrics.image.repo | string | `"docker.io/library/telegraf"` | Telegraf image repository |
-| app-metrics.image.tag | string | `"1.30.2-alpine"` | Telegraf image tag |
+| app-metrics.image.repo | string | `"ghcr.io/lsst-sqre/telegraf"` | Telegraf image repository |
+| app-metrics.image.tag | string | `"nightly-alpine-2025-01-09"` | Telegraf image tag |
 | app-metrics.imagePullSecrets | list | `[]` | Secret names to use for Docker pulls |
 | app-metrics.influxdb.url | string | `"http://sasquatch-influxdb.sasquatch:8086"` | URL of the InfluxDB v1 instance to write to |
 | app-metrics.nodeSelector | object | `{}` | Node labels for pod assignment |

applications/sasquatch/charts/app-metrics/README.md

@@ -16,8 +16,8 @@ Kafka topics, users, and a telegraf connector for metrics events.
 | globalAppConfig | object | See `values.yaml` | app-metrics configuration in any environment in which the subchart is enabled. This should stay globally specified here, and it shouldn't be overridden.  See [here](https://sasquatch.lsst.io/user-guide/app-metrics.html#configuration) for the structure of this value. |
 | globalInfluxTags | list | `["application"]` | Keys in an every event sent by any app that should be recorded in InfluxDB as "tags" (vs. "fields"). These will be concatenated with the `influxTags` from `globalAppConfig` |
 | image.pullPolicy | string | `"Always"` | Image pull policy |
-| image.repo | string | `"docker.io/library/telegraf"` | Telegraf image repository |
-| image.tag | string | `"1.30.2-alpine"` | Telegraf image tag |
+| image.repo | string | `"ghcr.io/lsst-sqre/telegraf"` | Telegraf image repository |
+| image.tag | string | `"nightly-alpine-2025-01-09"` | Telegraf image tag |
 | imagePullSecrets | list | `[]` | Secret names to use for Docker pulls |
 | influxdb.url | string | `"http://sasquatch-influxdb.sasquatch:8086"` | URL of the InfluxDB v1 instance to write to |
 | nodeSelector | object | `{}` | Node labels for pod assignment |

applications/sasquatch/charts/app-metrics/values.yaml

@@ -41,12 +41,17 @@ cluster:
   name: sasquatch
 
 # These values refer to the Telegraf deployment and config
+# We are currently using a nightly build to get functionality that will be
+# released in 1.34, in March 2025. Once 1.34 has been released, we should
+# stop using this nightly build.
 image:
   # -- Telegraf image repository
-  repo: "docker.io/library/telegraf"
+  repo: "ghcr.io/lsst-sqre/telegraf"
+  #repo: "docker.io/library/telegraf"
 
   # -- Telegraf image tag
-  tag: "1.30.2-alpine"
+  tag: "nightly-alpine-2025-01-09"
+  # tag: "1.30.2-alpine"
 
   # -- Image pull policy
   pullPolicy: "Always"