Allow publishing cloud events directly

[suraciii]

Description

Please explain the changes you've made

Allow users to publish cloud events directly, so that users can specify attributes (types, subjects, etc), which are useful for events routing.

This PR added two types, CloudEvent and CloudEvent<TData>.

Usage:

var objectDeletedCloundEvent = new CloudEvent<ObjectDeleted>(new(objectName))
{
	Source = new Uri("https://example.com/storage/" + bucketName),
	Type = "com.example.object.deleted.v2",
	Subject = "mynewfile.jpg",
};
await daprClient.PublishEventAsync("mypubsub", "mytopic", objectDeletedCloundEvent);

The result message content in kafka:

{
	"id": "a4c2d9ee0-275c-4c7b-8de7-0d2e71ff942f",
	"data": {
		"objectName": "myfile.jpg"
	},
	"datacontenttype": "application/json",
	"source": "https://example.com/storage/mybucket",
	"type": "com.example.object.deleted.v2",
	"subject": "mynewfile.jpg",
	"traceid": "00-c01e688aeea66df6a18b5f3f7748c74a-27785df64ee3b34c-01",
	"traceparent": "00-c01e688aeea66df6a18b5f3f7748c74a-27785df64ee3b34c-01",
	"tracestate": "",
	"topic": "mytopic",
	"pubsubname": "mypubsub",
	"specversion": "1.0"
}

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #[issue number]
#773

Checklist

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

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[halspang]

Thanks for opening this PR! Overall, everything looks good. One thing I think it'd be good to investigate is to see if we can mimic the tests here:

https://github.com/dapr/dotnet-sdk/blob/master/test/Dapr.AspNetCore.IntegrationTest/CloudEventsIntegrationTest.cs

Using the updated client. Can you look into that and see if there's value there?

[codecov]

Codecov Report

Merging #868 (d20159b) into master (2651832) will increase coverage by 0.03%.
The diff coverage is 92.30%.

@@            Coverage Diff             @@
##           master     #868      +/-   ##
==========================================
+ Coverage   69.13%   69.16%   +0.03%     
==========================================
  Files         142      143       +1     
  Lines        4649     4657       +8     
  Branches      517      520       +3     
==========================================
+ Hits         3214     3221       +7     
  Misses       1318     1318              
- Partials      117      118       +1     

Flag	Coverage Δ
net5	69.12% <92.30%> (+0.03%)	⬆️
net6	69.12% <92.30%> (+0.03%)	⬆️
netcoreapp3.1	69.12% <92.30%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/Dapr.Client/DaprClientGrpc.cs	87.70% <80.00%> (-0.18%)	⬇️
src/Dapr.Client/CloudEvent.cs	100.00% <100.00%> (ø)

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[suraciii]

@halspang Thanks for your review.

I think events published by dapr client are encapsulated by dapr runtime, so tests on test/Dapr.AspNetCore.IntegrationTest/CloudEventsIntegrationTest.cs (the consumer side) should not be able to cover the behavior of dapr client.

Please correct me if I have misunderstood that.

[saber-wang]

Can this RP be merged? This function is required