Limit count query in the events APIs

What does this MR do and why?

This change limits the count query for events to 10,000. The query provides the total count used for the X-Total and X-Total-Pages headers. When the offset exceeds 10,000, these headers are not returned. This limitation improves query performance for large datasets.

See the related discussion #357839 (comment 2119565466).

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Query plans

• Before - https://console.postgres.ai/gitlab/gitlab-production-main/sessions/31705/commands/98222
• After - https://console.postgres.ai/gitlab/gitlab-production-main/sessions/31705/commands/98220

How to set up and validate locally

Go to https://gdk.test:3000/api/v4/projects/30/events.

Related to #357839