metrics-probe: add new parser which generates stats counters

[alltilla]

This kind of parser counts messages passing through, based on the metadata of each message. It creates labeled stats counters based on the fields of the message. Both the key and labels can be set in the config, the values of the labels can be templated.

Both the key and labels can be set in the config, the values of the labels can be templated. E.g.:

parser p_metrics_probe {
  metrics-probe(
    key("custom_key")  # adds "syslogng_" prefix => "syslogng_custom_key"
    labels(
      "custom_label_name_1" => "foobar"
      "custom_label_name_2" => "${.custom.field}"
    )
  );
};

With this config, it creates counters like these:

syslogng_custom_key{custom_label_name_1="foobar", custom_label_name_2="bar"} 1
syslogng_custom_key{custom_label_name_1="foobar", custom_label_name_2="foo"} 1
syslogng_custom_key{custom_label_name_1="foobar", custom_label_name_2="baz"} 3

The minimal config creates counters with the key syslogng_classified_events_total and labels app, host, program and source. E.g.:

parser p_metrics_probe {
  metrics-probe();

  # Same as:
  #
  # metrics-probe(
  #   key("classified_events_total")
  #   labels(
  #     "app" => "${APP}"
  #     "host" => "${HOST}"
  #     "program" => "${PROGRAM}"
  #     "source" => "${SOURCE}"
  #   )
  # );
};

With this config, it creates counters like these:

syslogng_classified_events_total{app="example-app", host="localhost", program="baz", source="s_local_1"} 3
syslogng_classified_events_total{app="example-app", host="localhost", program="bar", source="s_local_1"} 1
syslogng_classified_events_total{app="example-app", host="localhost", program="foo", source="s_local_1"} 1

Depends on #4325

Signed-off-by: Attila Szakacs szakacs.attila96@gmail.com

[github-actions]

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[kira-syslogng]

Build FAILURE

[alltilla]

@kira-syslogng retest this please

[MrAnno]

This is great :)

[MrAnno]

LGTM.

[MrAnno]

👍🏻👍🏻