New pattern submission - appsync-lambda-s3-presigned-urls-pipeline-resolver

[mate329]

To submit a template to the Serverless Patterns Collection, submit an issue with the following information.

IMPORTANT
Patterns are intended to be primarily IaC-focused implementations of 2-4 AWS services, with minimum custom code. They should be commonly used combinations that help developers get started quickly. If you have a utility, demo, or application, submit these to the Serverless Repos Collection instead.

ONLY SUBMIT ONE PATTERN CHANGE PER PR. Multiple patterns or files spanning multiple pattern directories will be automatically rejected.

Patterns may take up to 4-6 weeks to review, test, and merge but there is no SLA and can take significantly longer due to other work the team has.

To learn more about submitting a pattern, read the publishing guidelines page.

1. Use the model template located at https://github.com/aws-samples/serverless-patterns/tree/main/_pattern-model to set up a README, template and any associated code.

2. THIS PROCESS HAS BEEN SIMPLIFIED. All the information below must be provided in the "example-pattern.json" file cloned from the model **

Note the following information for the model:

• Description (intro.text) should be a 300-500 word explanation of how the pattern works.
  This sample project demonstrates how AWS AppSync pipeline resolvers orchestrate multiple data sources within a single GraphQL operation, integrating AppSync with Lambda, DynamoDB, and S3 to create a notes API with secure file attachments. When a note is created via the saveNote mutation, the pipeline resolver invokes a Lambda function to generate a presigned S3 upload URL and then stores the note metadata—including the attachment key and upload URL—in DynamoDB, allowing the client to receive both the note data and a temporary upload URL in one response for immediate file upload. When retrieving a note through the getNote query, the resolver first reads the note from DynamoDB and then conditionally calls Lambda to generate a presigned download URL if an attachment exists, showcasing how pipeline resolvers execute conditional logic and pass data between stages using $ctx.prev.result. The pattern deploys a single AppSync GraphQL API, one Lambda function, one DynamoDB table, and one S3 bucket with proper CORS configuration.

• Resources should like to AWS documentation and AWS blogs related to the post (1-5 maximum).
  AWS AppSync Pipeline Resolvers - https://docs.aws.amazon.com/appsync/latest/devguide/pipeline-resolvers.html
  Amazon S3 Presigned URLs - https://docs.aws.amazon.com/AmazonS3/latest/userguide/PresignedUrlUploadObject.html
  AWS AppSync - Build data-driven apps with fully managed GraphQL APIs - https://aws.amazon.com/appsync/
  VTL Mapping Templates for AppSync - https://docs.aws.amazon.com/appsync/latest/devguide/resolver-mapping-template-reference.html

• Author bio may include a LinkedIn and/or Twitter reference and a 1-sentence bio.
  Cloud Engineer @ Elixirr Digital, LinkedIn - https://www.linkedin.com/in/matiarasetina/
  You must ensure that the sections of the model README.md are completed in full.

GitHub PR for template: #2859