docs: add one more scenario to when vault fails to write logs
Inspired by the scenario seen in 2023-10-31: firing - Vault audit log request fa... (gitlab-com/gl-infra/production#17056 - closed)
Inspired by the scenario seen in 2023-10-31: firing - Vault audit log request fa... (gitlab-com/gl-infra/production#17056 - closed)