[jk] Pipeline runs table (for individual pipelines) updates

[johnson-mage]

Description

• Add Started at column to Pipeline Runs table.
• Add search input for searching pipeline run variables on Pipeline Runs page for individual pipelines.

How Has This Been Tested?

"Started at" column included in Pipeline Runs table:

Searching for substring in key or value in pipeline runs' variables:

Checklist

• The PR is tagged with proper labels (bug, enhancement, feature, documentation)
• I have performed a self-review of my own code
• I have added unit tests that prove my fix is effective or that my feature works
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation