feat(remix): Set sentry-trace <meta> on server-side.

[onurtemizkan]

Ref: #4894

Remix provides a meta function to set <meta> tags for route modules.
This PR adds a meta function to each route to set sentry-trace using the http.server (root) span.

[Lms24]

This is looking good although my knowledge about Remix is still limited. We discussed this briefly at our meeting today and I have two requests:

• can we add another tag with the name baggage for baggage/dynamic sampling context propagation?
  This data should always be sent in combination with the sentry-trace data because only together we can correctly sample traces (for dynamic sampling). I'm realizing that we probably didn't communicate this correctly (apologies for that). I think the change should be fairly small. (I marked the position where I think we need to add a few lines in a comment).
  For more information on baggage see here (this is how it should look in the meta tags) and here

• can we add a few tests to make sure this change is covered?

[Lms24]

So just to confirm, this adds a meta tag to the html that looks as follows?:

<meta name="sentry-trace" content="..." />

[onurtemizkan]

Yes, that's correct. (docs) Also tested manually. 👍

[Lms24]

RE: baggage meta tag

Don't take this suggestion literally (e.g. still needs imports and all) but I think this is how it could work.

Slightly above, get the active transaction (from the scope) and then here:

Suggested change

	'sentry-trace': span.toTraceparent(),
	'sentry-trace': span.toTraceparent(),
	baggage: serializeBaggage(transaction.getBaggage()),

[onurtemizkan]

@Lms24, thanks a lot for the review!

Added the baggage 👍

One question to confirm this update is reflecting correctly on dashboard:

Is this what we expect (pageload as the child of http.server)?

About the tests, IMHO it'll be a bit hard to unit test this without importing the actual Remix library (at least lots of types from it). Would it be OK if we test this (and whole instrumentServer) with the integration tests which I think is my next chunk of work?

[Lms24]

Is this what we expect (pageload as the child of http.server)?

Chatted with @lobsterkatie about it: This seems about right 👍

Would it be OK if we test this (and whole instrumentServer) with the integration tests

Good point, yes let's wait for integration tests for now!