in_prometheus_textfile: new plugin to read .prom metric files

[edsiper]

This PR introduces a new input plugin for Fluent Bit that scrapes metrics from text files written in the Prometheus exposition format. It mimics the behavior of Prometheus’ textfile collector, enabling users to ingest custom metrics from .prom files and forward them through the Fluent Bit pipeline.

• Supports reading .prom files with Prometheus-style metric definitions.
• Periodically scans specified file paths or glob patterns.
• Parses and converts metrics into Fluent Bit-compatible data.
• Compatible with Prometheus tooling and custom exporters that emit text-based metrics.
• Useful for exposing one-off or custom metrics from scripts and external processes.

service:
  flush: 1
  log_level: info

pipeline:
  inputs:
    - name: prometheus_textfile
      path: /var/lib/metrics/*.prom
      scrape_interval: 5s

  outputs:
    - name: stdout
      match: "*"

note: path supports glob patterns like *.prom.

Fixes: #10595 #10486

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

[cosmo0920]

BTW, the test data for reading runtime tests for prometheus_textfile is missing in this PR?

[edsiper]

@cosmo0920 yeah good catch, I forgot to add the test data file :D , just added it

[edsiper]

s390x :/

[cosmo0920]

s390x :/

No worries, 19 - flb-it-input_chunk (Failed) is some times flaky on s390x.