feat(appsync): support enumeration types for code-first approach

[BryanPan342]

Support Enum Types for code-first approach. Enum Types are special types of Intermediate Types in CDK.

Desired GraphQL Enum

enum Episode {
  NEWHOPE
  EMPIRE
  JEDI
}

The above GraphQL Enumeration Type can be expressed in CDK as the following:

CDK Code

const episode = new appsync.EnumType('Episode', {
  definition: [
    'NEWHOPE',
    'EMPIRE',
    'JEDI',
  ],
}); 
api.addType(episode);

Discussion on the addField API can be found here.

---

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addressed suggestions

[BryanPan342]

[NOTE]

A discussion was had offline discussing the addField function in the IIntermediateType interface.

aws-cdk/packages/@aws-cdk/aws-appsync/lib/schema-base.ts

Lines 166 to 169 in 5861f07

	/**
	* Add a field to this Intermediate Type
	*/
	addField(options: AddFieldOptions): void;

Some of the concerns that were brought to light in this PR was that causing a synth error is bad for the user because users could easily get punished for using the a weakly-typed API.

We ultimately decided to continue with the AddFieldOptions struct as an input for addField for a couple of reasons:

• jsii prevents us from using generics and unions
• All intermediate types should have a shared interface, having a separate addField for every single Intermediate Type is impractical
• IIntermediateType must have an addField function to allow for dynamic schema generation
  • the addType function returns IIntermediateType
  • IntermediateTypes instantiated through the addType would be unable to addField if the function didn't exist in the interface

  const type = api.addType(new ObjectType(definition));
  type.addField(fieldName, field);   // this would be impossible if the addField function isn't in `IIntermediateType`

addressed

[mergify]

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[aws-cdk-automation]

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• CodeBuild project: AutoBuildProject6AEA49D1-qxepHUsryhcu
• Commit ID: af44256
• Result: SUCCEEDED
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[mergify]

Thank you for contributing! Your pull request will be updated from master and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).