[Feature Request] Support RDS Proxy as an AppSync data source

We have multiple production API deployments, having ~500 Lambda resolvers on average.

1. Most of the 500 functions are thin resolvers, only for the purpose of interacting with RDS Proxy with an Aurora Serverless V2 cluster behind it. It adds significant latency overhead because of Lambda cold starts, with our Node.js TypeScript stack it increases response time with ~1.4s.
2. Some of our older deployments use Aurora Serverless V1, they are constantly impacted by the slower scaling window, resulting in "Too Many Connections" error.

These problems would be solved if AWS AppSync supports RDS Proxy as a datasource out of the box, without having to go through Lambda.

Start by reviewing AWS AppSync data-source capabilities and how RDS Proxy connects to Aurora Serverless V1 and V2. There are no repository files or tests identified; done would require a decided implementation or service-level support for using RDS Proxy directly as an AppSync data source without Lambda resolvers.

Written by the indexing model from the issue text.