chore: replace partition promtail with alloy

[ma-hartma]

Description

Replaces promtail with alloy in the partition.
There is an own PR for the control-plane replacement: #595.

• deploy alloy
  • role for docker service in partition (switches and management servers)
• convert existing configs
  • convert existing scrape configs with alloy convert and re-templated them
  • provide as snippets
  • multiple loki targets
  • timeouts and basic auth for loki targets
• logs and metrics for alloy itself (https://grafana.com/docs/alloy/latest/collect/metamonitoring/=) to loki and prometheus
  • partition
  • document prometheus_alloy targets
• positions file
• old labels

Question Marks:

• prometheus inside the partition could be replaced with alloy completely as it can pick up the metrics as well, but aggregation would have to be re-evaluated

After successful replacement

• update monitoring docs for the website
• migration guide
  • (mention https://grafana.com/docs/alloy/latest/set-up/migrate/from-promtail/#limitations)
• mini-lab uses alloy instead of promtail (WIP chore: replace control-plane and partition promtail with alloy mini-lab#298)
• deprecate promtail roles

Manually tested in mini-lab:

• syslog snippet
• syslog snippet with positions file
• journal snippet
• docker snippet
• journal-file snippet with /run/log/journal and /var/log/journal
• journal-file snippet with positions file, missing positions name and existing positions name
• alloy-meta snippet
• metrics are collected via prometheus
• labels as expected (logs and alloy metrics)
• cutover migration from promtail to alloy in the mini-lab with existing positions files and stopping promtail

References:

• chore: replace control-plane promtail with alloy #595 control-plane promtail->alloy migration
• chore: replace control-plane and partition promtail with alloy mini-lab#298 to test this in the mini-lab
• docs(monitoring): use alloy instead of promtail website#260 website docs update
• chore: add alloy image releases#287 add image to releases
• Sflow integration #584 will have to replace promtail as well

Closes #552

Used AI-Tools ✨

• Claude Sonnet 4.6 for docs and migration guide generation and jinja templating

Release Notes

Required Actions

The partition `promtail` role is deprecated and replaced by the new `alloy` role. Operators should migrate to Alloy for partition log collection.

Follow the migration instructions: https://github.com/metal-stack/metal-roles/blob/master/partition/roles/alloy/README.md#migration-from-promtail

Several migration scenarios are supported — from a hard cutover to a parallel run for verification before switching over. Note that running both services simultaneously will produce duplicate log entries in Loki during the transition window.

[Gerrit91]

You put a lot of thought into it, which I enjoy. Also things are implemented very thoughtfully. It just could be a bit less complex here and there to my taste. :D

[ma-hartma]

You put a lot of thought into it, which I enjoy. Also things are implemented very thoughtfully. It just could be a bit less complex here and there to my taste. :D

Thanks for the extensive review!
Well, it was my first Ansible role and I haven't used it before, so maybe I took some things too serious! :D
I'll try to apply your proposed changes ASAP to be able to get the PR into the next release.