[8.x](backport #41061) Use journald for system module on Debian 12

[mergify]

Proposed commit message

This commit adds Debian 12 support to our system module, to support
Debian 12 we need to use the journald input to collect the system
logs.

To support it, a new, internal, input system-logsis introduced, it is responsible
for deciding whether the log input or journald must be used. If var.paths is defined
in the module configuration, system-logs looks at the files, if any of the globs resolves
to one or more files the log input is used, otherwise the jouranld input is used.

This behaviour can be overridden by setting var.use_journald or var.use_files,
which will force the use of journald or files.

Other changes:

• Journald input now support filtering by facilities
• System tests for modules now support handling journal files
• The TESTING_FILEBEAT_FILEPATTERN environment variable now is a
  comma separated list of globs, it defaults to .log,*.journal
• Multiple lint warnings are fixed
• The documentation has been updated where needed.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

• Debian 12 is now supported by Filebeat's system module
• On Debian 12 the system module will use the journald input
• The ingest pipelines for the system module were modified from 1 per fileset to 3
• The journald input currently only reads logs from the current boot

## Author's Checklist

How to test this PR locally

Run the tests

mage buildSystemTestBinary
mage docker:ComposeUp
source $(mage PythonVirtualEnv)/bin/activate
INTEGRATION_TESTS=1 BEAT_STRICT_PERMS=false ES_PASS=testing ES_USER=admin TESTING_FILEBEAT_MODULES=system pytest tests/system/test_modules.py

Run the system module

Package Filebeat from this PR.
Start the Debian 12 VM, run Filebeat

vagrant up debian12
vagrant ssh debian12
cp /vagrant/filebeat/build/distributions/filebeat-oss-9.0.0-SNAPSHOT-linux-x86_64.tar.gz ./
tar -xf filebeat-oss-9.0.0-SNAPSHOT-linux-x86_64.tar.gz 
cd filebeat-9.0.0-SNAPSHOT-linux-x86_64/
./filebeat modules enable system
./filebeat setup -e -v
# edit modules.d/system.yml and enable both filesets
# edit filebeat.yml and add the ES output and Kibana URL/credentials
./filebeat -e -v

Ensure data is ingested (datastream filebeat-9.0.0)

Related issues

• Closes Investigate the best way to decide when to read system logs from files or journald #40526

## Use cases
## Screenshots
## Logs

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This is an automatic backport of pull request #41061 done by [Mergify](https://mergify.com).

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