feat: add angular codegen v6 support

[AaronZyLee]

Description of changes

Added angular codegen support for JS V6

The new users will have the amplifyJsLibraryVersion with default value as 6 in their .graphqlconfig.yml file when running amplify codegen add and selecting the angular target.

The old v5 angular users are not impacted as the config file is not modified. To opt-in the new codegen, they can run amplify codegen remove and amplify codegen add with the same angular option as target.

The old v5 angular is still available by editing the .graphqlconfig.yml file to switch the amplifyJsLibraryVersion from 6 to 5.

The other inputs in this field are invalid with warning message and will fall into the v6 codegen behavior.

Changes for angular codegen v6 include:

• New import for aws-amplify/api and rxjs

import { Injectable } from "@angular/core";
import { Client, generateClient, GraphQLResult } from "aws-amplify/api";
import { Observable } from "rxjs";

• Queries, mutations and subscriptions use the generateClient to execute APIs

export class APIService {
  public client: Client;
  constructor() {
    this.client = generateClient();
  }

  async GetTodo(id: string): Promise<GetTodoQuery> {
    //...
    const response = (await this.client.graphql({
      query: statement,
      variables: gqlAPIServiceArguments
    })) as any;
    return <GetTodoQuery>response.data.getTodo;
  }

  async CreateTodo(
    input: CreateTodoInput,
    condition?: ModelTodoConditionInput
  ): Promise<CreateTodoMutation> {
    //...
    const response = (await this.client.graphql({
      query: statement,
      variables: gqlAPIServiceArguments
    })) as any;
    return <CreateTodoMutation>response.data.createTodo;
  }

  OnCreateTodoListener(
    filter?: ModelSubscriptionTodoFilterInput
  ): Observable<GraphQLResult<Pick<__SubscriptionContainer, "onCreateTodo">>> {
    //...
    return this.client.graphql({
      query: statement,
      variables: gqlAPIServiceArguments
    }) as any;
  }
}

Codegen Paramaters Changed or Added

New target angularv6 in typegen

Issue #, if available

Fix #783

Description of how you validated changes

• Unit and E2E tests
• Test new codegen with an angular sample app

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)
• Breaking changes to existing customers are released behind a feature flag or major version update
• Changes are tested using sample applications for all relevant platforms (iOS/android/flutter/Javascript) that use the feature added/modified
• Changes are tested on windows. Some Node functions (such as path) behave differently on windows.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[phani-srikar]

We previously had tests for when this new config property is undefined and we added unit tests for V6, can you also add a test when it's set to v5?

[elaf2001]

Could you provide an estimate on when the team plans to review and potentially merge this code? It would be helpful for those of us interested in the feature to have an idea of the timeline. Thank you!

[iartemiev]

Giving admin approval for API.md changes, did not review the rest of the PR