feat(sveltekit): Add SvelteKit client and server init functions

[Lms24]

This PR adds SDK init functions for the SvelteKit SDK server- and client-side. Currently these functions

• set SDK metadata
• call the respective base SDK's init
• set a runtime tag ('browser' / 'node' resp.)

Also fixed a bug in the Svelte SDK where passed in options._metadata.sdk was previously overwritten with the Svelte SDKs data.

ref #7348

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.24 KB (+0.12% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	62.95 KB (+0.11% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.87 KB (+0.1% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	55.87 KB (+0.12% 🔺)
@sentry/browser - Webpack (gzipped + minified)	20.62 KB (+0.12% 🔺)
@sentry/browser - Webpack (minified)	67.39 KB (+0.1% 🔺)
@sentry/react - Webpack (gzipped + minified)	20.65 KB (+0.12% 🔺)
@sentry/nextjs Client - Webpack (gzipped + minified)	48.54 KB (+0.18% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	27.51 KB (+0.23% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.76 KB (+0.21% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	43.17 KB (+0.01% 🔺)
@sentry/replay - Webpack (gzipped + minified)	37.19 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	61.18 KB (+0.09% 🔺)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	54.35 KB (+0.04% 🔺)