⚠️ BREAKING CHANGE ⚠️

PR Description

Enables running multiple instances of Promtail in the same way one can run multiple instances of Prometheus. This is a breaking change. Configs in this form:

loki:
  positions:
    filename: /tmp/positions.yaml
  clients:
    - url: http://loki:3100/loki/api/v1/push
  scrape_configs:
  - job_name: system
    static_configs:
      - targets:
        - localhost
        labels:
          job: varlogs
          __path__: /var/log/*log

must be rewritten to be in this new form:

loki:
  configs:
  - name: default
    positions:
      filename: /tmp/positions.yaml
    clients:
      - url: http://loki:3100/loki/api/v1/push
    scrape_configs:
    - job_name: system
      static_configs:
        - targets:
          - localhost
          labels:
            job: varlogs
            __path__: /var/log/*log

Which issue(s) this PR fixes

Closes #313.

Notes to the Reviewer

Lots to do still. Opening this up in draft to get early feedback based on the versioning approach.

TODO:

• Need to update the Promtail dependency so we can pass custom Prometheus registerers to each Promtail (done by update cortex, loki #355)
• Needs a lot of testing, maybe add an agent-all-in-one.yaml to cmd/agent for local testing.
• Positions file directory should be created on startup with 0700 permissions.

PR Checklist

• CHANGELOG updated
• Documentation added
• Tests updated