feat(a11y): add aria-label support for upload buttons in SSH keys forms (#1534)

Add optional uploadButtonAriaLabel prop to TextFileUpload component to improve screen reader accessibility. The component now allows consumers to set descriptive aria-labels on upload buttons, making it clearer what file type is being uploaded.

Apply this enhancement to SSH private and public key upload buttons in the Add SSH Keys modal, providing context-specific labels for better accessibility.

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: vinokurig