feat: Enable hide_credentials for multi-auth plugin

[madhawa-gunasekara]

Current implementation supports hide_credentials in the auth_plugin sub plugin level, but in that case users can't use same header name for multiple authentication.
example :
plugins: multi-auth: auth_plugins: - basic-auth: { } - jwt-auth: cookie: jwt query: jwt header: authorization - key-auth: query: apikey header: authorization