fix: use /flags endpoint for nextjs rewrites

[joshsny]

We want to use the new flags endpoint in rewrite configurations

[Copilot]

Pull Request Overview

This PR updates NextJS rewrite configurations to use the new /flags endpoint instead of the deprecated /decide endpoint. The change aligns the documentation and test configurations with the updated API endpoint.

• Updates documentation examples to use /ingest/flags instead of /ingest/decide
• Simplifies the test application configuration by removing PostHog-specific rewrites

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/nextjs/docs.ts	Updates three NextJS configuration examples to use the new /flags endpoint in rewrite rules
e2e-tests/test-applications/nextjs-instrumentation-client-test-app/next.config.ts	Simplifies configuration by removing PostHog rewrites and reverting to basic NextJS config

Comments suppressed due to low confidence (1)

e2e-tests/test-applications/nextjs-instrumentation-client-test-app/next.config.ts:2

• The removal of PostHog rewrites from the test application configuration may break existing e2e tests that depend on the /ingest/flags endpoint being properly routed. Consider adding back the rewrite rules with the updated /flags endpoint to maintain test coverage.

const nextConfig = {};

[daniloc]

nice, makes sense to me!