IClientConfig should provide APIs to support arbitrary typed values

[allenxwang]

Currently IClientConfig only supports storing and retrieving configuration values as String, and a few convenience APIs to convert them to limited types like Integer and Boolean. It requires user to know the actual data type associated with each config key, and pays a conversion cost when the value is retrieved.

It would be nice for IClientConfig and DefaultClientConfigImpl to support arbitrary configuration values in an intuitive way.

Here is the proposal:

• Associate a generic type for each common configuration key.
• Add new APIs in IClientConfig to support retrieving values with the generically typed configuration key.
• Reserve the behavior to read configuration values as string from Archaius and convert them to desired type on demand.

Here is the code example to show desired behavior:

    public static final IClientConfigKey<Integer> ReadTimeout = ...

    int readTimeout = clientConfig.getPropertyWithType(IClientConfigKey.CommonKeys.ReadTimeout);

[allenxwang]

Added in Ribbon 2 release.