profiler: add FlushAndStop to upload current profiles before exiting

[jinroh]

What does this PR do?

This PR adds a new bool env DD_PROFILING_FLUSH_ON_EXIT in order to abort and upload the current profiling sessions before exiting.

Motivation

• profiling short lived processes without fine-tuning the period
• profile visibility on the "exit section" of processes and applications

Reviewer's Checklist

• [ ] Changed code has unit tests for its functionality at or near 100% coverage.
• [ ] System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• [ ] There is a benchmark for any new code, or changes to existing code.
• [ ] If this interacts with the agent in a new way, a system test has been added.
• [ ] Add an appropriate team label so this PR gets put in the right place for the release notes.
• [ ] Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

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[pr-commenter[bot]]

Benchmarks

Benchmark execution time: 2024-10-14 15:29:59

Comparing candidate commit b17b58a2002cc91a571fba27e3ed1ab1f4a2ed45 in PR branch jinroh/profiler-flush-and-stop with baseline commit 5b9a8af2b241ec60b990840add9da5799c3c811b in branch main.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 57 metrics, 1 unstable metrics.

scenario:BenchmarkInjectW3C-24

• 🟩 execution_time [-181.063ns; -146.537ns] or [-4.224%; -3.418%]