Refactor clone dropdown

What does this MR do and why?

Follow-up issue for Migrate dropdown to new gl dropdown components (!121951 - merged)

• move the gl-disclosure-dropdown-item into a new component
• add some additional tests
• add a storybook story for the component

Related to #413482 (closed)

Screenshots or screen recordings

• No visual changes to the component
• New storybook story added

Both links	SSH Link	HTTPS link

How to set up and validate locally

Run the jest tests:

$ yarn jest clone_dropdown

View the storybook stories:

$ yarn storybook:start

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.