Reduce SDS timeout for secret push protection to allow time for gem-based fallback

Summary

Currently, the Secret Detection Service (SDS) gRPC call in secret push protection uses the default timeout of 180 seconds. This is problematic because:

1. If SDS becomes slow or unresponsive, users experience very long delays during git push operations
2. There's insufficient time remaining for the gem-based fallback to complete within reasonable push timeouts
3. Without back-pressure handling on the SDS side, requests can pile up during traffic bursts

Related

• !210620 (merged) - Use the SDS hosted on runway for GitLab.com
• !210620 (comment 2871265638) (discussion with @vbhat161)