feat: add emptyText to SelectArrayInput

[SurendraKumawat7742]

Problem

SelectArrayInput does not currently support the emptyText prop, so users cannot provide an empty option in the dropdown to clear all selected values.

Solution

• Add support for the emptyText prop to SelectArrayInput.
• Render emptyText as an empty option in the dropdown.
• Translate string values consistently with other choice inputs.
• Clear the selected values by calling onChange([]) when the empty option is selected.
• Add a unit test covering the new behavior.

How To Test

• Run : npx jest packages/ra-ui-materialui/src/input/SelectArrayInput.spec.tsx --runInBand
• Expected result : Test Suites: 1 passed, 1 total , Tests: 37 passed, 37 total

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

Also, please make sure to read the contributing guidelines.