[Agent] Fixed injected log path to monitoring beat

[michalpristas]

What does this PR do?

Incorrect path was passed to monitoring beat so it could not pick up files from log directory

Why is it important?

To enable logs monitoring

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.

How to test

Package agent and run standalone with this config

outputs:
  default:
    type: elasticsearch
    hosts: [127.0.0.1:9200]
    username: elastic
    password: changeme
datasources:
- id: system-1
  enabled: true
  use_output: default
  inputs:
  - type: system/metrics
    enabled: true
    streams:
    - id: system/metrics-system.core
      enabled: true
      dataset: system.core
      period: 10s
      metrics:
      - percentages
    - id: logs-system.syslog
      enabled: true
      dataset: system.syslog
      paths:
      - "/var/log/messages*"
      - "/var/log/syslog*"
  package:
    name: system
    version: 0.9.0  
settings.monitoring:
  use_output: default
  enabled: true
  logs: true
  metrics: true
management:
  mode: "local"
  fleet:
    access_token: ""
    kibana:
      host: "localhost:5601"
      ssl.certificate_authorities: ["/etc/pki/root/ca.pem"]
  reporting:
    log:
      format: "default"
    fleet:
      enabled: false
      reporting_threshold: 10000
      reporting_check_frequency_sec: 30
  reload:
    enabled: true
    period: 10s
download:
  sourceURI: "https://artifacts.elastic.co/downloads/beats/"
  target_directory: "${path.data}/downloads"
  timeout: 30s
  pgpfile: "${path.data}/elastic.pgp"
  install_path: "${path.data}/install"
process:
  min_port: 10000
  max_port: 30000
  spawn_timeout: 30s
retry:
  enabled: true
  retriesCount: 3
  delay: 30s
  maxDelay: 5m
  exponential: false

when you check GET /_cat/indices/ in kibana you should see filebeat-8.0.0-{date} index created.

[elasticmachine]

Pinging @elastic/ingest-management (Project:fleet)