Add dd-trace-filter

[Qard]

What does this PR do?

Adds dd-trace-filter, which is a msgpack binary-to-binary transformer to apply truncation and (eventually) obfuscation logic in a way which can easily be shared across libraries.

Motivation

This was a R&D Week project to see if it would be reasonable to build something in WASM to filter msgpack encoded trace chunks to truncate long fields and obfuscate anything that needs obfuscating.

[ivoanjo]

So... My rust-foo is definitely not great to help out with the actual code side.

On the other hand, it seems harmless to me for us to merge this in -- worse thing we can move or remove it at some later point in the future. Do you mind updating the README with a bit of context on what this is?

I'm otherwise happy to approve. Or, you can try chasing people down in slack to get an actual review of the code :D

[Qard]

I'm not in a huge rush to merge immediately. I just opened a PR mainly to have something for people to look at. It's still somewhat in-progress though. I can find a bit of time soon to do a bit more cleanup and land then. It should at least probably be passing the CI before it lands. Don't want to interfere with CI on other PRs. 😅

[ivoanjo]

Yes, definitely fix CI first haha I was kinda assuming that as a given, I'm not that crazy ;) ;)

[dbenamydd]

Guess this is stale :-) Please reopen if not!