Enhance Sidebar component accessibility

[morinokami]

Motivation and Context

This PR improves accessibility in the Sidebar component by adding

• proper htmlFor attributes to all form labels that reference the corresponding input/select elements
• matching id attributes to all form controls (inputs, selects) to associate them with their labels
• aria-label attributes to environment variable key and value inputs to provide proper labeling context
• aria-expanded attributes to all collapsible section toggle buttons (Environment Variables, Authentication, Configuration) to indicate their current state

How Has This Been Tested?

I confirmed the label associations work in the browser and visually inspected the accessibility tree to verify proper values are set.

Breaking Changes

None.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update