NR-55461 Add Prometheus Agent quickstart

[marcsanmi]

Summary

Add Prometheus Agent quickstart.

For context, we developed the New Relic Prometheus Configurator in order to simplify the experience configuring features like discovery, filtering, metrics decoration, and sharding. The configurator generates a configuration file that is used to run a Prometheus Server in Agent mode.

Pre merge checklist

• [X] Did you check you NRQL syntax? - Does it work?
• [X] Did you include an InstallPlan and Documentation reference?
• [X] Are all documentation links publically accessible?
• [X] Did you check your descriptive content for voice and tone?
• [X] Did you check your descriptive content for spelling and grammar errors?

Dashboards

• [X] Does the PR contain a screenshot for each of your dashboards?
• [X] Do your screenshots show data?
• [X] Has the sanitization script been run on each dashboard?

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- prometheus-agent

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[paologallinaharbur]

https://github.com/newrelic/newrelic-quickstarts/pull/1503 has been mergerd, I am re-triggering the pipeline and testing again

EDIT I cannot trigger it again 😢