4.x: JFR documentation guide

[romain-grecourt]

Environment Details

• Helidon Version: 4.x
• Helidon SE and Helidon MP

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Problem Description

Add guides for using JFR with Helidon SE and Helidon MP.

I.e. Steps for:

• Adding code to generate JFR events
• Running the application to capture data
• Observing the captured data

See https://www.morling.dev/blog/rest-api-monitoring-with-custom-jdk-flight-recorder-events for inspiration.

[danielkec]

Also soon to be the only correct way of monitoring pinned virtual threads