fix docker container name extraction in fluent bit

[Polliog]

Fixes #269

Problem

The shipped Fluent Bit pipeline has a Copy container_name service filter, but nothing ever set container_name: extract_container_id.lua only extracted the container ID from the log filepath (/var/lib/docker/containers/<ID>/<ID>-json.log), and the container name simply is not part of that path. The copy was a silent no-op, so logs reached LogTide with no service field at all and only container_id/container_short_id in metadata, which is what showed up in the UI.

Fix

extract_container_id.lua now resolves the container name from the container's config.v2.json, which Docker keeps next to the log file and which is already available through the existing read-only /var/lib/docker/containers mount in both compose files (no compose changes needed):

• the name is matched with an anchored pattern ("Name":"/<name>"); container names always carry the leading slash there, so volume mount Name keys in the same file cannot be picked up by mistake
• results are cached per container ID, so the file is read once per container, not once per record
• when config.v2.json is missing or unreadable, container_name falls back to the 12-char short ID, so service is always populated

Verification

Tested end-to-end against the real fluent/fluent-bit:4.2.2 image with the repo's parsers.conf, the production filter chain and a fake /var/lib/docker/containers tree (one container with a config.v2.json including a decoy volume Name, one without the file):

Before (current main): records had no service at all.

After:

{"service":"my-test-container","container_id":"aaaa...ffff","container_short_id":"aaaaaaaaaaaa","message":"hello from named container\n","level":"info",...}
{"service":"111111111111","container_id":"1111...6666","container_short_id":"111111111111","message":"hello from nameless container\n","level":"info",...}

container_name is still stripped from the final record by the existing record_modifier filter, and the backend ingest fallback chain (service || container_name || ... || 'unknown') is untouched.

[codecov]

Codecov Report

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