Fix to accept correct JSON schema of response from AWS AppConfig

[lavenderses]

What

Bugfix for valid JSON response schema

close #19

How

• Changed AttributeParser (Parser interface for T-typed feature flag value from AWS AppConfig JSON response) to expect following JSON schema.
  • By change to implement Function, not BiFunction

Previously, BiFunction accepts whole JSON response and following JSON. But actually they were same.
So, simply unified the args to keyNode arg.

{
  // "Add new flag" > "Create flag" > "Off" or "On"
  "enabled": boolean,
  // "Add new flag" > "Create flag" > "Attribute (optional)"
  "flag_value": number | string | boolean | regex,
}

Notes

N/A

[lavenderses]

LGTM