build(cdn): Make integration CDN bundles build in parallel

[mydea]

I noticed we have a --parallel flag for building the integration CDN addons, but don't use it. At least locally that drastically improves build time for me (from ~250s to ~70s).

While at it I also aligned the JS version strings we use there in rollup with the browser config.

[AbhiPrasad]

This reminds me of a certain 2006 hit animated sports comedy film.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.57 KB (0%)
@sentry/browser - ES5 CDN Bundle (minified)	64.2 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.13 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified)	56.58 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	21.59 KB (0%)
@sentry/browser - Webpack (minified)	71.66 KB (0%)
@sentry/react - Webpack (gzipped + minified)	21.61 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	51.95 KB (+0.14% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	27.93 KB (-0.01% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	26.1 KB (-0.01% 🔽)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	44.37 KB (0%)
@sentry/replay - Webpack (gzipped + minified)	38.44 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	62.59 KB (-0.01% 🔽)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	56.1 KB (-0.01% 🔽)