APIAccessChecker: Refactor and simply plugin implementation using better data structures

Signed-off-by: Rohit Yadav <bhaisaab@apache.org>
APIChecker: Rename refactor and add interface checkExistence

Signed-off-by: Rohit Yadav <bhaisaab@apache.org>
ApiDiscoveryServiceImpl: Implement listApis to return response based on role

Signed-off-by: Rohit Yadav <bhaisaab@apache.org>