Handle "client_payload is too large"

follow up to https://github.com/octokit/openapi/issues/301

We will need to truncate `client_payload` if necessary. I had to do it in another internal project, I can re-use the same code here

Start by reviewing how this GitHub Action constructs and sends client_payload, then read the linked octokit/openapi issue #301 for the size constraint. The work is done when oversized client_payload data is truncated as needed without breaking the release notification flow.

Written by the indexing model from the issue text.