Dynamic Sampling Context / Baggage continuation - #1485

GET /api/shows/?q=test HTTP/1.1
sentry-trace: 29fe0a09960b4c06b3d60d7dd653b5eb-96813dbb300bb498-1
baggage: sentry-environment=dev,sentry-release=0.0.1,sentry-transaction=%2Fapi%2Fshows%2F%3Fq%3Dtest,sentry-user_id=278612,sentry-user_segment=Some%20segment%20(485744)%7D,sentry-public_key=e39cc598149f46899082d1348c4abac1,sentry-trace_id=29fe0a09960b4c06b3d60d7dd653b5eb,sentry-sample_rate=1

(Pdb) headers.get('baggage')
'sentry-environment=dev,sentry-release=0.0.1,sentry-transaction=%2Fapi%2Fshows%2F%3Fq%3Dtest,sentry-user_id=970676,sentry-user_segment=Some%20segment%20(763434)%7D,sentry-public_key=e39cc598149f46899082d1348c4abac1,sentry-trace_id=ad113195e0614ecca6598645db4114bd,sentry-sample_rate=1'

(Pdb) envelope.headers["trace"]
{'trace_id': 'a207344557f04656bb7aeff10c725312', 'public_key': 'e39cc598149f46899082d1348c4abac1', 'sample_rate': '1', 'release': '0.0.1', 'environment': 'dev', 'transaction': '/api/shows/?q=tes', 'user_id': '970676', 'user_segment': 'Some segment (763434)}'}