fix(js/browser): Amend user IP + sendDefaultPii change to v10 migration guide

[Lms24]

Mentions a fix to be introduced in 10.4.0 in the migration guide given it has quite a lot of impact, albeit belated (should have been like this since v9).

This change is now mentioned in:

• 10.4.0 changelog
• in-repo migration guide
• in-docs migration guide (this PR)

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
sentry-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 11, 2025 9:30am

1 Skipped Deployment

Name	Status	Preview	Comments	Updated (UTC)
develop-docs	⬜️ Ignored (Inspect)	Visit Preview		Aug 11, 2025 9:30am

[codecov]

Bundle Report

Changes will increase total bundle size by 870 bytes (0.0%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
sentry-docs-client-array-push	9.85MB	-6 bytes (-0.0%) ⬇️
sentry-docs-server-cjs	12.38MB	876 bytes (0.01%) ⬆️

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	1.77MB	-0.0%
../instrumentation.js	-3 bytes	1.1MB	-0.0%
9523.js	-3 bytes	1.08MB	-0.0%
../app/[[...path]]/page.js.nft.json	295 bytes	745.38kB	0.04%
../app/platform-redirect/page.js.nft.json	295 bytes	745.29kB	0.04%
../app/sitemap.xml/route.js.nft.json	295 bytes	742.76kB	0.04%

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	882.71kB	-0.0%
static/chunks/8321-*.js	-3 bytes	425.87kB	-0.0%
static/kzR_z16xnwCCtDFQAZVRX/_buildManifest.js (New)	684 bytes	684 bytes	100.0% 🚀
static/kzR_z16xnwCCtDFQAZVRX/_ssgManifest.js (New)	77 bytes	77 bytes	100.0% 🚀
static/OyMpO1gIKXV2rF4F-*.js (Deleted)	-684 bytes	0 bytes	-100.0% 🗑️
static/OyMpO1gIKXV2rF4F-*.js (Deleted)	-77 bytes	0 bytes	-100.0% 🗑️