`journald` input should pass `--all` to `journalctl`

[ioanrogers]

Describe the enhancement:

While trying out the journald with our internal application logs we noticed a number of log events where message == null. This intentional behaviour from journalctl for fields > 4096 bytes and can be fixed by passing --all

It would be great if journald could pass this arg, perhaps optionally.

Here's a similar issue: open-telemetry/opentelemetry-collector-contrib#30920

Describe a specific use case for the enhancement or feature:

Not losing log info when using journald input with reasonably sized JSON messages.

Thanks!

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)