Add support for x scope org id header in loki source api

[QuentinBisson]

PR Description

This pull request introduces a middleware for extracting tenant headers in the loki PushAPIServer to improve tenant context handling.

Which issue(s) this PR fixes

Notes to the Reviewer

PR Checklist

• CHANGELOG.md updated
• Documentation added
• Tests updated
• Config converters updated

[QuentinBisson]

I also added tests :)

[mattdurham]

Can we add documentation to the loki.source.api component?

[QuentinBisson]

@mattdurham do you want me to document the use of the header? Sure I will do that tomorrow at the latest

[mattdurham]

Yes, maybe something like we did with scrape https://grafana.com/docs/alloy/latest/reference/components/prometheus/prometheus.scrape/#technical-details

@clayton-cornell would be the expert on how this should be organized.

[clayton-cornell]

Lets keep it simple. If it's a technical description of how things work and what to expect... then following the prometheus.scrape example should work. I'll review and if there's structural changes we can either do it in this PR or merge this one and I'll rework in a new (whichever is easiest).

[QuentinBisson]

@clayton-cornell Could you check if the documentation is alright?

[clayton-cornell]

I think the docs are OK for this PR.

I will open up an issue on the layout and structure of the Technical details section. I think it's at the wrong level in the topic hierarchy... here and in prometheus.scrape. Instead of blocking this PR for the doc fixes, let's merge and I'll fix things in a separate doc-only PR.

[QuentinBisson]

Thanks for the help :)

[mattdurham]

LGTM