[EuiBadge] Add button type to prevent form submission

[thompsongl]

Summary

Fixes #4273 by adding type=button to the "remove" button on the EuiBadge items rendered by EuiComboBox.
The problem comes from the default button type=submit being triggered when Enter was hit on an input element in a form with onSubmit/action.

What should happen? The onSubmit handler of the form should be triggered, the combo box should not react at all

This is half true. The combobox should indeed not react, but the form should not submit without a type=submit element in the form. The spec says that in a form with no submit buttons, implicit submission will be done if only one input is present.

So you can see in the to-be-reverted docs change that the combobox no longer steals focus, but the form will not be submitted without uncommenting the submit input.

Checklist

- [ ] Check against all themes for compatibility in both light and dark modes
- [ ] Checked in mobile

• Checked in Chrome, Safari, Edge, and Firefox

- [ ] Props have proper autodocs and playground toggles
- [ ] Added documentation

• Checked Code Sandbox works for the any docs examples

- [ ] Added or updated jest tests

• Checked for breaking changes and labeled appropriately
• Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_4479/

[chandlerprall]

LGTM! Pulled & tested locally, including with & without the extra text input and/or submit button. Form submission only happened when expected.

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_4479/