GDEV-378: adding support for request configuration

[darlanmoraes]

usage:

module "appsync" {
  graphql = {
    schema = var.graphql_schema
    target = {
      lambda = aws_lambda_function.default[0].arn
      merge  = var.appsync_merged_api_id
    }
    authentication = {
      type      = var.graphql_authentication_type
      user_pool = var.cognito_user_pool
    }
    resolvers = [{
      type  = "Mutation"
      field = "myMutation"
    }]
  }

  transform = {
    request = {
      type = "with-claims"
    }
  }
}