[receiver/journald] Handle MESSAGE field more conveniently

[fuero]

Component(s)

No response

What happened?

Description

MESSAGE might be an byte array, if journald thinks there's a non-printable character inside:

journalctl -xe CONTAINER_NAME=logging-test -o json | jq -crs .[].MESSAGE
[72,101,108,108,111,32,87,111,114,108,100,33,13]

The journald receiver forwards this as-is.

Steps to Reproduce

Do printf("Hello World!") from inside a docker container and let its logs be pushed to otel-collector

Expected Result

Forward the log line as unicode string, not byte array. Let the exporter take care of shipping it to the destination correctly.
Otherwise, processing steps become more complex

Actual Result

See above

Collector version

0.111.0

Environment information

Environment

OS: Debian Bookworm
Release: otelcol-contrib debian package

OpenTelemetry Collector configuration

# Relevant portion only
receivers:
  journald:
    directory: /var/log/journal

Log output

{
        "PRIORITY" : "6",
        "_SOURCE_REALTIME_TIMESTAMP" : "1729708971622850",
        "_SYSTEMD_UNIT" : "docker.service",
        "_HOSTNAME" : "xxx",
        "_BOOT_ID" : "78032dd089a94f00b81a810ba32fbd6d",
        "_SYSTEMD_CGROUP" : "/system.slice/docker.service",
        "_CAP_EFFECTIVE" : "1ffffffffff",
        "_CMDLINE" : "/usr/sbin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock",
        "MESSAGE" : [
                72,
                101,
                108,
                108,
                111,
                32,
                87,
                111,
                114,
                108,
                100,
                33,
                13
        ],
        "CONTAINER_ID" : "30ef3e4a2e9a",
        "_GID" : "0",
        "CONTAINER_TAG" : "30ef3e4a2e9a",
        "_COMM" : "dockerd",
        "_SYSTEMD_INVOCATION_ID" : "1450b926b1474106a9ea6af9f5aa3b0a",
        "__MONOTONIC_TIMESTAMP" : "116279775072",
        "CONTAINER_ID_FULL" : "30ef3e4a2e9a541792564c957d8570a70d387134d0d1098807524b1183568c34",
        "_UID" : "0",
        "_PID" : "3548",
        "_SYSTEMD_SLICE" : "system.slice",
        "IMAGE_NAME" : "openjdk:21",
        "_MACHINE_ID" : "5cd5aae0da034744beac106810fdd968",
        "_EXE" : "/usr/sbin/dockerd",
        "CONTAINER_NAME" : "logging-test",
        "SYSLOG_IDENTIFIER" : "30ef3e4a2e9a",
        "__REALTIME_TIMESTAMP" : "1729708971623225",
        "_RUNTIME_SCOPE" : "system",
        "_TRANSPORT" : "journal",
        "_SELINUX_CONTEXT" : "unconfined\n",
        "__CURSOR" : "s=84d41b02e4994e1b82d490a999839343;i=8ea3ed;b=78032dd089a94f00b81a810ba32fbd6d;m=1b12d08f60;t=6252940d18339;x=c2f5ce410bd3c45b"
}

Additional context

No response