feat: AWS Lambda authorizer support

[diegocstn]

Description of changes:
This PR introduces the changes to support for AWS Lambda authorizer.
Customers will be able to use the new AWS_LAMBDA authorization type by providing an instance of a type conforming to the AWSLambdaAuthProvider protocol, similarly to as they currently do for OIDC.

Example of dx:

struct MyAuthProvider: AWSLambdaAuthProvider {
    func getLatestAuthToken() -> String {
        "custom-lambda-token"
    }
}
``

let authProvider = MyAuthProvider()
let serviceConfig = try AWSAppSyncServiceConfig()
let config = try AWSAppSyncClientConfiguration(
    appSyncServiceConfig: serviceConfig,
    awsLambdaAuthProvider: authProvider)

let appSyncClient = try AWSAppSyncClient(appSyncConfig: config)

References
Amplify iOS PR: aws-amplify/amplify-swift#1334
Amplify Android PR: aws-amplify/amplify-android#1412
AppSync SDK Android PR: awslabs/aws-mobile-appsync-sdk-android#358

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[royjit]

LGTM, only concern I had is regarding inheriting the protocol AWSLambdaAuthProvider from AWSOIDCAuthProvider. Please provide comments on why it was done so

[diegocstn]

@royjit The idea was to re-use the OIDC interceptor given that they both just add a token as the authorization header value. Changed to use a custom interceptor as I did for Amplify and removed the protocol conformance.
I'm gonna create a story to refactor the auth interceptors across packages. I believe we can re-use some code there.