feat(combobox): make the title collapsible

[YiyangLi]

Hi, I want to add a feature to combox, specifically making the group label collapsible. We are not able to use groupLabelTemplate to simply add an interactive button. Because we are not able to "hide" the children items under the group.

Contributing to Twilio

All third-party contributors acknowledge that any contributions they provide will be made under the same open-source license that the open-source project is provided under.

• [x] I acknowledge that all my contributions will be made under the project's license.