Use async pipeline creation on git push by default

Vasilii Iakliushinrequested to merge
558015-async-pipeline-creation-by-default into master

What does this MR do and why?

Contributes to #558015 (closed)

The feature flag was enabled since 2025-08-14 and appears stable.

Problem

The Ci::CreatePipelineService runs synchronously and can take significant time to complete, which slows down the PostReceive job and degrades overall performance.

Solution

Execute the Ci::CreatePipelineService task asynchronously.

MR acceptance checklist

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

Related to #558015 (closed)

Merge request reports