Add support for USDT tracepoints in VAST

[lava]

📔 Description

See extensive description in the new header file itself.

📝 Checklist

• All user-facing changes have changelog entries.
• The changes are reflected on docs.tenzir.com/vast, if necessary.
• The PR description contains instructions for the reviewer, if necessary.

🎯 Review Instructions

Review all commits at once.

To verify that release builds now contain trace points by default:

1. Download the CI artifact on a linux system
2. Use sudo perf buildid-cache -a /path/to/libvast.so to add the binary to the buildid cache
3. Use sudo perf probe --list | grep vast to see if the tracepoint exist
   (optionally)
4. Use e.g. sudo perf probe sdt_vast:chunk_make and perf record -e sdt_vast:chunk_make -- vast start to record the samples

[dominiklohmann]

This requires Folly to be added to our Open-Source Licenses document. Do you want me to make this change?

[dominiklohmann]

lgtm modulo passive voice in the changelog.