fix(node): attach local req scope to req.sentryScope

[derN3rd]

This PR:

• Attaches the scope of the domain context inside of a request to req.sentryScope
• Adds a test to check if req.sentryScope is defined

Fixes #4607

[derN3rd]

I guess this should be also added to the docs, if this will make it into master.
https://docs.sentry.io/platforms/node/guides/express/

Will add a PR to sentry-docs afterwards

[AbhiPrasad]

Hey thanks for opening a PR! We're gonna chat about this as a team (pinged everyone as appropriate), and then we can come back and figure out how to proceed

[AbhiPrasad]

We are currently discussing if this would be beneficial over const scope = Sentry.getCurrentHub().getScope() - which should effectively do the same thing.

Thoughts?

[derN3rd]

Didn't notice that Sentry.getCurrentHub() is domain-aware in node envs, will try that.

If I remember correctly, I saw some issues with that in async contexts, like express-apis are, also here in the repo.
But I will try the suggested solution first in our production environment and see if there are any issues with not correctly matched data (also with my solution)

Thanks!