Enhance: Limit GRPC Endpoint

## Description

Currently we have GetBlocks api limit open. Meaning client can set the limit to whatever number they want, and this will sometime take the node down.

Set a limit on the `limit` parameter passed by client, so that the node will not accept for more than 500.

## Breakdown
- Limit GetBlocks API


## Expected behavior
A brief description of what you expected to happen.