### Description

`TransportGrantAction` currently provides an `executeWithGrantAuthentication` method which sub-classes can leverage. Instead of requiring sub-classes to invoke this method directly, we instead can move it into the `doExecute` method of `TransportGrantAction`, and allow inheritors to specify their own handler for grant authentication, something along the lines of: 

```
class TransportGrantAction {

    final void doExecute(...) {
        // executeWithGrantAuthentication can furthermore be inlined as part of this refactor
        executeWithGrantAuthentication(request, ActionListener.wrap(
            authentication -> { doSomethingWithAuthentication(...) }
        ));
    }

    abstract doSomethingWithAuthentication(...);
}
```

This reduces boilerplate and establishes a clearer contract for sub-classes of `TransportGrantAction`.
x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/action/TransportGrantAction.java
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0; you may not use this file except in compliance with the Elastic License
 * 2.0.
 */
package org.elasticsearch.xpack.security.action;
import org.elasticsearch.ElasticsearchSecurityException;
import org.elasticsearch.ElasticsearchStatusException;
import org.elasticsearch.action.ActionListener;
import org.elasticsearch.action.ActionResponse;
import org.elasticsearch.action.support.ActionFilters;
import org.elasticsearch.action.support.HandledTransportAction;
import org.elasticsearch.common.io.stream.Writeable;
import org.elasticsearch.common.util.concurrent.ThreadContext;
import org.elasticsearch.rest.RestStatus;
import org.elasticsearch.transport.TransportService;
import org.elasticsearch.xpack.core.security.action.GrantRequest;
import org.elasticsearch.xpack.core.security.action.user.AuthenticateAction;
import org.elasticsearch.xpack.core.security.action.user.AuthenticateRequest;
import org.elasticsearch.xpack.core.security.authc.Authentication;
import org.elasticsearch.xpack.core.security.authc.AuthenticationServiceField;
import org.elasticsearch.xpack.core.security.authc.AuthenticationToken;
import org.elasticsearch.xpack.security.authc.AuthenticationService;
import org.elasticsearch.xpack.security.authz.AuthorizationService;
public abstract class TransportGrantAction<Request extends GrantRequest, Response extends ActionResponse> extends HandledTransportAction<