fix(nextjs): Respect PORT variable for dev error symbolication

[chargome]

Next.js respects the PORT variable. If for some reason this is not sufficient for users we can ship a follow up with a config option, which I wanted to avoid in the first step.

Also did a small refactor of the fetching code.

closes #18135
closes https://linear.app/getsentry/issue/JS-1139/handle-the-case-where-users-define-a-different-portprotocol

[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	8,867	-	8,820	+1%
GET With Sentry	1,388	16%	1,402	-1%
GET With Sentry (error only)	6,161	69%	6,079	+1%
POST Baseline	1,215	-	1,214	+0%
POST With Sentry	524	43%	525	-0%
POST With Sentry (error only)	1,082	89%	1,065	+2%
MYSQL Baseline	3,331	-	3,369	-1%
MYSQL With Sentry	491	15%	496	-1%
MYSQL With Sentry (error only)	2,724	82%	2,757	-1%

View base workflow run

[linear]

JS-1139 Handle the case where users define a different port/protocol