Implement FormFieldset Wrapper Component

[jenny-s51]

Introduce FormFieldset component to provide consistent MUI-themed inputs for Patternfly form elements, similar to the one used in kubeflow/model-registry.

Why It's Needed:

• Replicates MUI’s outlined-field DOM structure (fieldset + legend)
• Ensures consistent borders, spacing and overall styling across all form inputs
• Applies MUI's DOM structure to PatternFly form components
• Leverages our existing MUI theme to style every form element for a unified look and feel

[jenny-s51]

/assign

[jenny-s51]

/area frontend

[jenny-s51]

/area v2