### 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/apikey/TransportGrantApiKeyAction.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.apikey;
import org.elasticsearch.action.ActionListener;
import org.elasticsearch.action.support.ActionFilters;
import org.elasticsearch.common.inject.Inject;
import org.elasticsearch.common.util.concurrent.ThreadContext;
import org.elasticsearch.tasks.Task;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.transport.TransportService;
import org.elasticsearch.xcontent.NamedXContentRegistry;
import org.elasticsearch.xpack.core.security.action.apikey.CreateApiKeyResponse;
import org.elasticsearch.xpack.core.security.action.apikey.GrantApiKeyAction;
import org.elasticsearch.xpack.core.security.action.apikey.GrantApiKeyRequest;
import org.elasticsearch.xpack.security.action.TransportGrantAction;
import org.elasticsearch.xpack.security.authc.ApiKeyService;
import org.elasticsearch.xpack.security.authc.AuthenticationService;
import org.elasticsearch.xpack.security.authc.support.ApiKeyUserRoleDescriptorResolver;
import org.elasticsearch.xpack.security.authz.AuthorizationService;
import org.elasticsearch.xpack.security.authz.store.CompositeRolesStore;
/**
 * Implementation of the action needed to create an API key on behalf of another user (using an OAuth style "grant")
 */
public final class TransportGrantApiKeyAction extends TransportGrantAction<GrantApiKeyRequest, CreateApiKeyResponse> {