Promtail to set journal target symbolic priority

[gtrubach]

Hi!

Is your feature request related to a problem? Please describe.
I want to display journal logs in grafana by using promtail and loki. Promtail extracts logs fine but journal contains priority in number format, not symbolic. So if I use the following scrape config:

- job_name: systemd-journal
  journal:
    max_age: 12h
    labels:
      job: systemd-journal
    path: /var/log/journal
  relabel_configs:
  - source_labels:
    - __journal__systemd_unit
    target_label: systemd_unit
  - source_labels:
    - __journal_priority
    target_label: level

level will be numeric and grafana will show unknown log level for it.

Describe the solution you'd like
It would be great if numeric priority will be transformed to symbolic as it's done for syslog target. In this case I will be able to map it to level label which can be read by grafana and shown correctly.

Describe alternatives you've considered
I tried to set it up using pipelines but I wasn't successful in it.

Additional context
Note the level label (6 is an info):

[gtrubach]

It still will be cool to have it out of the box, but I managed to do a workaround using pipeline stage:

pipeline_stages:
- job_name: systemd-journal
  journal:
    max_age: 12h
    labels:
      job: systemd-journal
    path: /var/log/journal
  relabel_configs:
  - source_labels:
    - __journal__systemd_unit
    target_label: systemd_unit
  - source_labels:
    - __journal_priority
    target_label: level
  pipeline_stages:
  - template:
      source: level
      template: '{{ if eq .Value "0" }}{{ Replace .Value "0" "emerg" 1 }}{{ else if eq .Value "1" }}{{ Replace .Value "1" "alert" 1 }}{{ else if eq .Value "2" }}{{ Replace .Value "2" "crit" 1 }}{{ else if eq .Value "3" }}{{ Replace .Value "3" "err" 1 }}{{ else if eq .Value "4" }}{{ Replace .Value "4" "warning" 1 }}{{ else if eq .Value "5" }}{{ Replace .Value "5" "notice" 1 }}{{ else if eq .Value "6" }}{{ Replace .Value "6" "info" 1 }}{{ else if eq .Value "7" }}{{ Replace .Value "7" "debug" 1 }}{{ end }}'
  - labels:
      level: