Add experimental Java profiling instrumentation

[lrwh]

Summary

This change adds an experimental Java profiling instrumentation for the javaagent.

Included

• add instrumentation/profiling/library
• add instrumentation/profiling/javaagent
• start continuous JFR-based profiling on Java 17+ JVMs
• export JFR snapshots through pluggable adapters
• add Datakit profile exporter using multipart/form-data
• add file exporter for validation/debugging
• support otel.profiling.* config and legacy compatibility aliases
• support memory profiling overlay options
• add library tests, Java 17 JFR tests, file exporter agent test, and Datakit exporter agent test

Notes

• profiling currently requires Java 17+ with JFR available
• JDK 8 runtime does not support this profiling implementation
• trace export code path is not changed in this PR

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

liurui seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}