Support case insensitive cloudevent payloads and forward cloudevent props s headers

[IliasP91]

Description

Extend the existing CloudEvent Middleware to:

• Accept case insensitive cloudevent payloads
• Extend its options to forward cloudevent props as HTTP Request.Headers

This will make the middleware accept JSON payloads that are Pascal cases, as the default ASP Net core options already do. And add the option to forward all the cloud event properties that are not automatically forwarded by the Dapr sidecar as headers. I had a use case where I wanted to read the type of the event (not just filter it) in my handler and currently there is no way of doing it as the middleware just unfolds the cloudevent envelope and discards it.

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• [x] Code compiles correctly
• [x] Created/updated tests
• [x] Extended the documentation (NA in this case there's no section that describes the UseCloudEvents() method, happy to create one of you think its valuable. I have extended one of the examples though)

[IliasP91]

hi again, could someone have a look at this PR? I has been sitting there for a few months now...

[marcduiker]

@holopin-bot @IliasP91 Thank you Ilias!

[holopin-bot[bot]]

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