docs(js): Update Next.js instrumentation instructions

[chargome]

Updates the manual setup docs to reflect latest Next.js version.

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
sentry-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jan 30, 2025 11:45pm

2 Skipped Deployments

Name	Status	Preview	Comments	Updated (UTC)
changelog	⬜️ Ignored (Inspect)			Jan 30, 2025 11:45pm
develop-docs	⬜️ Ignored (Inspect)			Jan 30, 2025 11:45pm

[codecov]

Bundle Report

Changes will decrease total bundle size by 15 bytes (-0.0%) ⬇️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
sentry-docs-server-cjs	10.63MB	-9 bytes (-0.0%) ⬇️
sentry-docs-client-array-push	9.31MB	-6 bytes (-0.0%) ⬇️

Affected Assets, Files, and Routes:

view changes for bundle: sentry-docs-server-cjs

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
1729.js	-3 bytes	1.63MB	-0.0%
../instrumentation.js	-3 bytes	965.23kB	-0.0%
9523.js	-3 bytes	941.45kB	-0.0%

view changes for bundle: sentry-docs-client-array-push

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
static/chunks/pages/_app-*.js	-3 bytes	866.04kB	-0.0%
static/chunks/9557-*.js	-3 bytes	391.11kB	-0.0%
server/middleware-*.js	-5.55kB	1.0kB	-84.74%
server/middleware-*.js	5.55kB	6.55kB	555.3% ⚠️
static/MNmhnDeNhioPnSuLaUQ-*.js (New)	77 bytes	77 bytes	100.0% 🚀
static/MNmhnDeNhioPnSuLaUQ-*.js (New)	578 bytes	578 bytes	100.0% 🚀
static/Ak6VqBUz9CVsf9LmFsYOe/_buildManifest.js (Deleted)	-578 bytes	0 bytes	-100.0% 🗑️
static/Ak6VqBUz9CVsf9LmFsYOe/_ssgManifest.js (Deleted)	-77 bytes	0 bytes	-100.0% 🗑️