Update user behavior of adding inputs

Summary

Users will add inputs explicitly in the scheduled pipeline and in the run new pipeline page.

Definition of Done

• Users can add by selecting specific inputs explicitly.
• Preview inputs is out of scope of this issue. We could tackle it in the next iteration: Provide a way to preview inputs before running ... (#547857 - closed)

Details

Design spec

• Figma dev 🔗
• Design tab 👉

Roles involved

• Design
• Technical Writing
• Backend
• Frontend
• Test engineering

NOTE: When work is ready to be defined, please create appropriate sub-tasks.