Add search/filter functionality to "Select inputs" dropdown

What does this MR do and why?

This MR adds search/filtering functionality to the inputs dropdown.

References

• Add search/filter functionality to "Select inpu... (#594203 - closed)
• #533802 (comment 3166675233)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create a pipeline with multiple inputs by following the pipeline inputs documentation. For example:

   spec:
     inputs:
       environment:
         type: string
         options: ['dev', 'staging', 'production']
       deploy_type:
         type: string
         options: ['full', 'partial']
       # Add more inputs to test filtering

2. Navigate to CI/CD > Pipelines and click Run pipeline

3. Click on the "Select inputs" dropdown and verify the search field filters the list as you type

MR acceptance checklist

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