update compatibility information for dd-trace-js 3.0 release

[rochdev]

Update compatibility information for dd-trace-js 3.0 release.

What does this PR do?

Update compatibility information for dd-trace-js 3.0 release. This includes dropping support for Node 12 and documenting our OS support policy.

Motivation

Node 12 is end of life, and our OS support policy was never properly documented.

Additional Notes

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Reviewer checklist

• [ ] Review the changed files.
• [ ] Review the URLs listed in the Preview section.
• [ ] Check images for PII
• [ ] Review any mentions of "Contact Datadog support" for internal support documentation.

[github-actions[bot]]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/rochdev/dd-trace-js-3.0/profiler/enabling/nodejs
• https://docs-staging.datadoghq.com/rochdev/dd-trace-js-3.0/security_platform/application_security/setup_and_configure
• https://docs-staging.datadoghq.com/rochdev/dd-trace-js-3.0/tracing/trace_collection/compatibility/nodejs
• https://docs-staging.datadoghq.com/rochdev/dd-trace-js-3.0/tracing/trace_collection/dd_libraries/nodejs

[rochdev]

@hestonhoffman Looks like this is ready to be shipped, how do we get this merged?