[New docs] Convert `EuiComboBox` docs to docusaurus and storybook

[tkajtoch]

Summary

Convert the entire content of EuiComboBox component docs to docusaurus (text content) and storybook (stories for all examples).

Acceptance Criteria

• There should be stories created for all EuiComboBox examples available on the current docs site.
• The EuiComboBox docs text content should be converted to MDX and added to docusaurus docs pages
• Examples should use the StoryEmbed component and render the EuiComboBox stories to match what's available on the current docs site

[github-actions[bot]]

👋 Hi there - this issue hasn't had any activity in 6 months. If the EUI team has not explicitly expressed that this is something on our roadmap, it's unlikely that we'll pick this issue up. We would sincerely appreciate a PR/community contribution if this is something that matters to you! If not, and there is no further activity on this issue for another 6 months (i.e. it's stale for over a year), the issue will be auto-closed.

[tkajtoch]

This is not valid anymore. We decided not to use embeddable stories as component playgrounds. EuiComboBox docs are already converted to MDX.