doc(astro): Update middleware documentation

[Lms24]

This PR updates the middleware documentation in two places

• be more explicit in pointing out that trackClientIP should only be used in SSR/hybrid configs
• replace old name of the middleware factory function with the current (hopefully final) one

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	65.25 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	55.49 KB (+0.02% 🔺)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	30.98 KB (+0.03% 🔺)
@sentry/browser - Webpack (gzipped)	21.3 KB (+0.04% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	61.83 KB (+0.02% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	29.1 KB (+0.04% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	21.24 KB (+0.05% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	194.91 KB (+0.02% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	88.32 KB (+0.03% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	63.3 KB (+0.04% 🔺)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	31.81 KB (+0.03% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	65.61 KB (+0.01% 🔺)
@sentry/react - Webpack (gzipped)	21.34 KB (+0.03% 🔺)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	82.35 KB (+0.01% 🔺)
@sentry/nextjs Client - Webpack (gzipped)	48.13 KB (+0.02% 🔺)
@sentry-internal/feedback - Webpack (gzipped)	15.98 KB (+1.06% 🔺)