Replace promtail with Grafana Alloy

[sysvinit]

The documentation for Loki notes that promtail is considered feature complete, and future feature development will happen in Grafana Alloy. This change hence replaces promtail with Alloy in an equivalent configuration.

Note that Alloy is a swiss-army knife all-in-one tool, so it includes a significant amount functionality which we are not using here -- this is reflected by the 285MB binary size.

PL-129625

@flyingcircusio/release-managers

Release process

• Created changelog entry using ./changelog.sh

PR release workflow (internal)

• PR has internal ticket
• internal issue ID (PL-…) part of branch name
• internal issue ID mentioned in PR description text
• ticket is on Platform agile board
• ticket state set to Pull request ready
• if ticket is more urgent than within the next few days, directly contact a member of the Platform team

Design notes

• Provide a feature toggle if the change might need to be adjusted/reverted quickly depending on context. Consider whether the default should be on or off. Example: rate limiting.
• All customer-facing features and (NixOS) options need to be discoverable from documentation. Add or update relevant documentation such that hosted and guided customers can understand it as well.

Security implications

• Security requirements defined? (WHERE)
  • Changing the implementation of the log-shipping client
• Security requirements tested? (EVIDENCE)
  • Alloy is a significantly larger and more complex application. However, our Loki integration is still under active development, so this will be reviewed in more depth at a later time.