Hide pipeline filter when no pipeline exists

What does this MR do?

Fixes #325553 (closed). We're showing the "filtered search" on the pipelines-empty state even though no pipelines were available.

How to try out locally

• Create a new or go to a project without .gitlab-ci.yml
• Disabled "Default to Auto DevOps pipeline" in the CI/CD settings of your project http://localhost:3000/<group_name>/<project_name>/-/settings/ci_cd
• Go to CI/CD -> Pipelines (http://localhost:3000/<group_name>/<project_name>/-/pipelines

Screenshots (strongly suggested)

Before	After	With existing pipelines

Does this MR meet the acceptance criteria?

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