Add camel case scenario doc

docs/camel_case_scenarios.md

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+# Camel case scenarios
+
+## how to enabel camel-case in $select
+
+Given an OData service as following configuration (It's a non-Edm scenario):
+```C#
+builder.Services.AddControllers().AddOData(options => options.Select().Filter().OrderBy());
+```
+
+If you send request: 
+```C#
+https://localhost:7158/WeatherForecast
+```
+
+The response looks like:
+```json
+[
+ {
+ "date": "2022-02-08T14:56:26.7139132-08:00",
+ "temperatureC": -3,
+ "temperatureF": 27,
+ "summary": "Mild"
+ },
+
+ ...
+```
+
+The property name is camel case. However, if you have an OData $select query as:
+
+```
+https://localhost:7158/WeatherForecast?$select=summary
+```
+The response looks like:
+```json
+[
+ {
+ "Summary": "Cool"
+ },
+ {
+ "Summary": "Warm"
+ }
+...
+]
+
+```
+
+The property name is not camel-case. 
+
+## The root problem is that: 
+
+$select will generate a select expand wrapper, which will output the selected property as a 'dictionary'. The key of dictionary is the property name, the value of dictionary is the selected property value.
+In order to make the dictionary key as camel case, you have to config the 'DictionaryKeyPolicy` for JSON serializer.
+
+Here's the configuration:
+
+```C#
+builder.Services.AddControllers()
+ .AddJsonOptions(options =>
+ {
+ options.JsonSerializerOptions.DictionaryKeyPolicy = JsonNamingPolicy.CamelCase;
+ })
+ .AddOData(options => options.Select().Filter().OrderBy());
+```
+
+Now, 
+```
+https://localhost:7158/WeatherForecast?$select=summary
+```
+has the following response:
+
+```json
+[
+ {
+ "summary": "Cool"
+ },
+ {
+ "summary": "Warm"
+ },
+ {
+ "summary": "Chilly"
+ },
+ {
+ "summary": "Balmy"
+ },
+ {
+ "summary": "Balmy"
+ }
+]
+```