Dropdown component

[mikemazara]

Reference Issues or PRs

closes #68

What does this implement/fix?

Put a x in the boxes that apply

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features not to work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):
  Adds DropdownMenu to the Nebari registry with composable parts, trigger variants (default/text), optional expand icon support, stories, and tests.

Testing

• Did you test the pull request locally?
• Did you add new tests?

Documentation

Access-centered content checklist

Text styling

• The content is written with plain language (where relevant).
• If there are headers, they use the proper header tags (with only one level-one header: H1 or # in markdown).
• All links describe where they link to (for example, check the Nebari website).
• This content adheres to the Nebari style guides.

Non-text content

• All content is represented as text (for example, images need alt text, and videos need captions or descriptive transcripts).
• If there are emojis, there are not more than three in a row.
• Don't use flashing GIFs or videos.
• If the content were to be read as plain text, it still makes sense, and no information is missing.

Any other comments?

Added dropdown component. included optional expand icon slot with showicon boolean props for ease of use