[Reliability] HTTP Headers should be processed as IgnoreCase

[sima-zhu]

Customer reported issue: #5623

Http headers are case insensitive so our deserializer cannot depend on case sensitive properties.
The current proposal of fixing the issue from @anuchandy and @jianghaolu :

1. During code generation we know the types representing Http headers. The properties of these types will have @JsonProperty with lower-case value.
2. For azure-core HttpClient, we will define a contract that all the Http header names in response HttpHeaders type will be lowercase. For built-in netty and okhttp clients we will do this normalization when we receives a response. here:
   

   azure-sdk-for-java/sdk/core/azure-core-http-netty/src/main/java/com/azure/core/http/netty/NettyAsyncHttpClient.java

   Line 133 in 078c771

   reactorNettyResponse.responseHeaders().forEach(e -> headers.put(e.getKey(), e.getValue()));

3. The HttpResponseHeaderDecoder first serializes this normalized HttpHeaders (it’s a Map<String, String>) to json, now we have a json with all keys as lowercase, then we deserialize this json to generated Header type, which also has lowercase jsonProperty values.

[sima-zhu]

@jianghaolu Could you update here for the autorest change status?

[sima-zhu]

#5839

[sima-zhu]

Closed the one above and opened a new one below
#5841

[sima-zhu]

The annotation for JsonFormat does not work.
Now approach another way, add the feature config in JacksonAdaptor for header mapper only.
PR: #5844

[sima-zhu]

Merged in the fix 3e03bf2

[ghost]

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