feat(core): Add addIntegration utility

[mydea]

To make it easier to async add integrations later, which is useful e.g. for replay but also for other cases.

Now instead of:

const client = Sentry.getCurrentHub().getClient();
if (client && client.addIntegration) {
  client.addIntegration(new Sentry.Replay());
}

You can just do:

Sentry.addIntegration(new Sentry.Replay());

Relates to:

• feat(node): Add Fastify integration #9138
• feat(vue): Expose VueIntegration to initialize vue app later #9180

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	84.22 KB (-0.03% 🔽)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	31.41 KB (0%)
@sentry/browser - Webpack (gzipped)	22 KB (0%)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	78.78 KB (+0.02% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	28.6 KB (+0.04% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	21.01 KB (+0.05% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	254.47 KB (+0.04% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	86.75 KB (+0.11% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	62.44 KB (+0.16% 🔺)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	31.46 KB (+0.04% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	84.25 KB (-0.03% 🔽)
@sentry/react - Webpack (gzipped)	22.05 KB (0%)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	102.22 KB (-0.02% 🔽)
@sentry/nextjs Client - Webpack (gzipped)	50.99 KB (-0.01% 🔽)