feat: Model engines are collapsable within model selection dropdown

[imtuyethan]

In Model Menu in Threads

Figma: https://www.figma.com/design/DYfpMhf8qiSReKvYooBgDV/Jan-App-(3rd-version)?node-id=7480-134479&t=VU8rTIkBKXFb3X7S-4

• Cloud model: Show icon + is users haven't input any API key
• Default to: Expand models that users have downloaded or insert API key while collapse the rest.

In My Models page

Figma: https://www.figma.com/design/DYfpMhf8qiSReKvYooBgDV/Jan-App-(3rd-version)?node-id=5303-14532&t=hUj1k73d2gxmAfY4-4

• Default to: Expand models that users have downloaded or insert API key while collapse the rest.

[Van-QA]

@urmauur, the dropdown icon is overlapping with the scroll bar, not sure if this is expected or not, thank you