2.0.0rc6

Various fixes & improvements

• Restore original behavior by always creating a span (#3005) by @antonpirker
• Merge baggage headers (incoming and new created ones) (#3001) by @antonpirker
• Fix duplicate baggage headers in Celery integration introduced in SDK 2.0 (#2993) by @antonpirker
• Make it work with old and new newrelic versions (#2999) by @antonpirker
• docs: Update migration guide wording (#2987) by @colin-sentry
• docs: Tweak migration guide (#2979) by @colin-sentry
• Small updates to migration guide (#2911) by @colin-sentry
• Update CHANGELOG.md (51a906c1) by @sentrivana
• release: 1.45.0 (7570e39a) by @getsentry-bot