feat: add copy to clipboard as valid type to button-group

[shannenigans]

Description

Add icon-copy-to-clipboard as a valid item type in the ButtonGroup component. This
allows users to embed a copy-to-clipboard action directly within a button group
alongside existing item types (icon-button, icon-toggle-button, icon-file-input,
menu-dropdown).

Changes:

• Added IconCopyToClipboard interface with properties: id, text, textToCopy,
  copySuccessText, copyErrorText, disabled, and disabledReason
• Added onCopySuccess and onCopyFailure event handlers to ButtonGroupProps
• Created CopyToClipboardItem component that wraps InternalCopyToClipboard with
  tooltip support
• Updated ItemRuntime, Item, and InternalItem union types to include the new
  item type
• Wired up copy event handlers through internal.tsx and item-element.tsx

Related links, issue #, if available: n/a

How has this been tested?

• Verified TypeScript compilation with the new type additions
• Manually tested rendering a button group with an icon-copy-to-clipboard item
• Confirmed copy success/failure callbacks fire correctly
• Confirmed tooltip behavior matches other button group item types

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see [CONTRIBUTING.md](https://
  github.com/cloudscape-design/components/blob/main/CONTRIBUTING.md#public-apis).
• Changes do not include unsupported browser features, see
  [CONTRIBUTING.md](https://github.com/cloudscape-design/components/blob/main/CONTRIB
  UTING.md#browsers-support).
• Changes were manually tested for accessibility, see accessibility
  guidelines.

Security

• If the code handles URLs: all URLs are validated through [the checkSafeUrl
  function](https://github.com/cloudscape-design/components/blob/main/src/internal/util
  s/check-safe-url.ts).

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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