Failed to link subscription on startup: not implemented: SHOW SUBSCRIPTIONS

I'm getting the following error when trying to connect Kapacitor to InfluxDB (both running as Docker containers). When I disable subscriptions explicitly it seems to work, but why are subscriptions not working?

```
run: open server: open service *influxdb.Service: failed to link subscription on startup: not implemented: SHOW SUBSCRIPTIONS
```

InfluxDB version: 2.7
Kapacitor version: 1.6

Start by tracing Kapacitor's startup subscription-linking path and the SHOW SUBSCRIPTIONS query against InfluxDB 2.7; the issue names no source file or test. Confirm the compatibility behavior and define a tested outcome in which startup no longer fails unexpectedly.

Written by the indexing model from the issue text.