Prometheus WAL compression is always enabled

[MichaelThamm]

Bug Description

Prometheus 2.20.0 (compression became default) 2020-07-22. In the charm code, we add the storage.tsdb.wal-compression to the pebble plan based on the Juju config being set to true. We need to instead set --no-storage.tsdb.wal-compression if the user chooses to disable it. Alternatively, we can remove this Juju config entirely since it hasn't done anything forever.

To Reproduce

❯ jsshc prometheus prometheus-k8s/0 bash
root@prometheus-k8s-0:/# pebble plan
services:
prometheus:
summary: prometheus daemon
startup: enabled
override: replace
command: /bin/prometheus --config.file=/etc/prometheus/prometheus.yml --storage.tsdb.path=/var/lib/prometheus --web.enable-lifecycle --web.external-url=http://prometheus-k8s-0.prometheus-k8s-endpoints.prom.svc.cluster.local:9090 --web.route-prefix=/ --web.enable-remote-write-receiver --log.level=info --storage.tsdb.retention.time=15d --storage.tsdb.retention.size=0.8GB

jc prometheus-k8s metrics_wal_compression=true

root@prometheus-k8s-0:/# pebble plan
services:
prometheus:
summary: prometheus daemon
startup: enabled
override: replace
command: /bin/prometheus --config.file=/etc/prometheus/prometheus.yml --storage.tsdb.path=/var/lib/prometheus --web.enable-lifecycle --web.external-url=http://prometheus-k8s-0.prometheus-k8s-endpoints.prom.svc.cluster.local:9090 --web.route-prefix=/ --web.enable-remote-write-receiver --log.level=info --storage.tsdb.wal-compression --storage.tsdb.retention.time=15d --storage.tsdb.retention.size=0.8GB

Environment

Prometheus K8s charm in isolation

Relevant log output

.

Additional context

No response