[WebPubSub] add content_type for send* async methods in 1.1.0

[xingsy97]

Description

• Add parameter content_type for send_to_* methods. See sync version in [WebPubSub] Update 1.1.0 #34552
• Fix a minor comment issue in sync version

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
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[azure-sdk]

API change check

APIView has identified API level changes in this PR and created following API reviews.

azure-messaging-webpubsubservice

[msyyc]

/check-enforcer override