fix(node): Avoid duplicated `sentry-trace` and `baggage` headers on fetch requests

[github-actions]

Note

The pull request "fix(node): Avoid duplicated sentry-trace and baggage headers on fetch requests" was created by @Lms24 but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.

• wip
• use dedupe approach
• fix bug in baggage merging
• fix(node): Avoid duplicated sentry-trace and baggage headers on fetch requests

[linear-code]

JS-1998

[Lms24]

I still hate this mechansim :(