add missing JsonPropertyName to Data property

[NenadSteric]

without it you need to force the JsonSerializer to use camelCase with JsonSerializerOptions

Description

adds JsonPropertyName to make the casing consistent with the other properties.

This also makes it possible to use just Serialize without JsonSerializerOptions
as the pubsub json handling code in Dapr needs this property to be lowercase.

This problem had to be fixed during testing of the new Bulk-publish API
where I needed to serialize the CloudEvent classes manually without the DaprClient.

Issue reference

as discussed in
#976 and #944

Checklist

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

• Code compiles correctly
• Created/updated tests - no new tests necessary, existing ones are green
• Extended the documentation - fixes an oversight - wouldnt know where to document this

Please comment if any new tests or documentation needs to be created.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (99d874a) 66.42% compared to head (d698577) 66.42%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1000   +/-   ##
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  Coverage   66.42%   66.42%           
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  Files         171      171           
  Lines        5758     5758           
  Branches      626      626           
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  Hits         3825     3825           
  Misses       1784     1784           
  Partials      149      149           

Flag	Coverage Δ
net6	66.42% <ø> (ø)
net7	66.42% <ø> (ø)

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Files Changed	Coverage Δ
src/Dapr.Client/CloudEvent.cs	100.00% <ø> (ø)

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[NenadSteric]

@approvers-dotnet-sdk: anything else needed ?

[WhitWaldo]

@NenadSteric Thank you for your contribution!

Upon digging into this, the various Dapr clients utilize a JsonSerializerOptions initialized with new JsonSerializerOptions(JsonSerializerDefaults.Web). One of the characteristics of the Web defaults is the use of "camelCase" name formatting, meaning that even without the JsonPropertyName attribute, the default value used will be "dapr" even without specifying it as much.

Further, because a JsonPropertyName would override the JsonSerializerOptions, merging your PR would result in developers being unable to trivially change the name format even if they really wanted to for some reason.

As such, I'm going to go ahead and reject this PR because as the underlying intent is to use a camel-cased name and it's already doing that by default and in an easily overridable manner, we're already at the desired outcome without any changes at all.

That said, if you think I'm missing something, please feel free to re-open with any follow-ups and I'd be happy to re-engage!