fix(otel): Prevent baggage from being overwritten

[AbhiPrasad]

ref: #6713

We want to make sure that existing baggage is not overwritten when the Sentry Propagator sets the baggage header on the carrier. To do this, we defer to using the W3CBaggagePropagator to set the baggage header, and add the Sentry values by setting baggage via OpenTelemetry's baggage API.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.84 KB (-0.01% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	61.46 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.62 KB (+0.02% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	55 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	20.38 KB (0%)
@sentry/browser - Webpack (minified)	66.55 KB (0%)
@sentry/react - Webpack (gzipped + minified)	20.4 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	47.63 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	26.82 KB (+0.02% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.25 KB (-0.01% 🔽)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	43.04 KB (+0.01% 🔺)
@sentry/replay - Webpack (gzipped + minified)	38.25 KB (-0.01% 🔽)