Doc update: updated label topic, specifically the example

[achatterjee-grafana]

Based on feedback from the community. Verified with @owen-d.

[CLAassistant]

All committers have signed the CLA.

[oddlittlebird]

LGTM

[owen-d]

This should just change the job name here to not conflict in the following example, not add a new clause to this one.

scrape_configs:
 - job_name: system
   pipeline_stages:
   static_configs:
   - targets:
      - localhost
     labels:
      job: syslog
      __path__: /var/log/syslog
 - job_name: system <-------------- change to "apache" or similar
   pipeline_stages:
   static_configs:
   - targets:
      - localhost
     labels:
      job: apache
      __path__: /var/log/apache.log

I'd suggest "apache" as the new job name

[owen-d]

Oops, looked like the second commit just updated the new lines the first commit added, not the actual line which needed to be changed and is already present in the docs.

[owen-d]

This is the fix needed - feel free to adapt this PR if you'd like commit credit or we can merge that one: #3641