Default enable pipeline_name feature flag and add pipeline_name_search feature flag

What does this MR do and why?

Describe in detail what your merge request does and why.

Default enable the pipeline_name feature flag. Since searching/filtering pipelines by name is not ready yet, this MR also introduces a new pipeline_name_search feature flag.

We decided to default enable the pipeline_name feature flag instead of removing it to give customers the option to disable it if they are not happy with the pipeline name replacing the commit title on the pipeline list and details pages. In the meantime, solution validation (https://gitlab.com/gitlab-org/ux-research/-/issues/2268) will be conducted.

Relevant issues:

• pipeline_name rollout issue: #376095 (closed).
• Feature issue: #372538 (closed).

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