Update flag settings for context

Enable or disable a feature flag for a context based on its context kind and key. In the request body, the `setting` should be the variation value to set for the context. It must match the flag's variation type. For example, for a boolean flag you can use `"setting": true` or `"setting": false` in the request body. For a string flag, you can use `"setting": "existing_variation_value_to_use"`. Omitting the `setting` attribute from the request body, or including a `setting` of `null`, erases the current setting for a context. If you previously patched the flag, and the patch included the context's data, LaunchDarkly continues to use that data. If LaunchDarkly has never encountered the combination of the context's key and kind before, it calculates the flag values based on the context kind and key.