Add continueTrace function

[lforst]

Problem Statement

It would be cool for any unsupported frameworks and even for the SDK internally in higher order SDKs to have a function that continues a trace from a sentry-trace and baggage value and starts a new transaction.

Solution Brainstorm

Function signature:

interface continueTrace<V> {
  (traceInformation: { sentryTrace: string, baggage: string }, (tracedTransaction: Transaction) => V): V
}

Example:

export function handler(req, res, next) {
  return continueTrace({
    sentryTrace: req.headers["sentry-trace"],
    baggage: req.headers["baggage"]
  }, (transaction) => {
    transaction.seTag('foo', 'bar');
    return next()
  });
}

[AbhiPrasad]

Let's make this work like Python does https://docs.sentry.io/platforms/python/usage/distributed-tracing/custom-instrumentation/

No need to assume performance monitoring, just mutate tracing information.

[lforst]

Yea we can copy what python does except for taking headers. Saying headers is overly specific and you can propagate tracing information over other mechanisms than headers. (CLI args, env-vars, ...)

[Lms24]

I like the python approach insofar as we provide a continueTrace function taking an object with the information and we can expose additional helpers to extract the information from whatever source they can come from.

[HazAT]

Please update this internal slack conversation once this ships
https://sentry.slack.com/archives/C05ABS7V7PY/p1694704574720109?thread_ts=1694674634.442359&cid=C05ABS7V7PY