fix(#5181): make variant optional in Angular goab-file-upload-input

[Copilot]

variant was marked required: true in the Angular wrapper despite having a default value of "dragdrop" in the Svelte web component and being optional in React.

Before (the change)

@Input({ required: true }) variant!: GoabFileUploadInputVariant;

Angular consumers were forced to always specify variant, causing a compile error if omitted.

After (the change)

@Input() variant: GoabFileUploadInputVariant = "dragdrop";

variant is now optional and defaults to "dragdrop", consistent with the web component and React wrapper.

Make sure that you've checked the boxes below before you submit the PR

• I have read and followed the setup steps
• I have created necessary unit tests
• I have tested the functionality in both React and Angular.

Steps needed to test

Use goab-file-upload-input in Angular without specifying variant and confirm it renders as dragdrop without a compile error:

<goab-file-upload-input (onSelectFile)="handleFileChange($event)"></goab-file-upload-input>