Express a chararcter limit in the diff summary prompt
What does this MR do and why?
We get errors reported (https://new-sentry.gitlab.net/organizations/gitlab/issues/284381/events/b7a6cad001b6470c8064644b4c7939d0/) that when the response we got from AI is longer than 2056 characters, the MergeRequest::DiffLlmSummary
won't be created because validation will fail.
Let's try to prompt the AI to reduce the number of characters and check the number of errors after.
Related to: #428399 (closed)
Edited by Marc Shaw