feat(core): Add lifecycle hooks

[AbhiPrasad]

Closes #7343

This PR adds a basic schema for hooks in the SDK. They live on the client.

Currently there are three hooks defined, but none of them are implemented. They are beforeTransaction, transactionFinish, and beforeEnvelope.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.22 KB (+0.51% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	62.89 KB (+0.6% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.85 KB (+0.53% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	55.8 KB (+0.56% 🔺)
@sentry/browser - Webpack (gzipped + minified)	20.6 KB (+0.5% 🔺)
@sentry/browser - Webpack (minified)	67.32 KB (+0.5% 🔺)
@sentry/react - Webpack (gzipped + minified)	20.62 KB (+0.47% 🔺)
@sentry/nextjs Client - Webpack (gzipped + minified)	48.36 KB (+0.18% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	27.35 KB (+0.33% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.62 KB (+0.41% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	43.15 KB (+0.08% 🔺)
@sentry/replay - Webpack (gzipped + minified)	37.16 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	61.01 KB (+0.18% 🔺)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	54.31 KB (+0.16% 🔺)

[mydea]

I pushed some changes onto this branch to use generics for type safety. I tried it locally and it seems to give me correct type safety as long as you specify the generic. Not sure if there is a way to enforce to provide the generic, not infer it 😅 but you can at least opt into type safety this way, and as an additional plus you only need to edit/add new hook types in a single place now!

[mydea]

cc @AbhiPrasad & @lforst refactored this again based on our discussion, looks good now I think, and the tests should also cover this decently (both the client & testclient case)