Importing TimelineItem from .com and creating matching docs

[jonrohan]

This PR adds the TimelineItem component that was recently added to github/github#120332

I'm also documenting the new component on primer.style

TODO on dotcom

• Remove components/timeline-item.scss

/cc @primer/ds-core

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[shawnbot]

This looks great! Let's queue it up for inclusion in 13.1.0, assuming we don't decide to move forward with 14.0.0.

[shawnbot]

@jonrohan let's roll the min-width: 0 fix into this PR before merging into #911 into 13.1.0

[shawnbot]

@jonrohan it looks like this isn't being imported anywhere in the product bundle. I'm stumped as to why this actually works on the docs site, though. 🤔

Either way, it's not present in dist/primer.css from the most recently published canary release, so let's fix that before merging.

[simurai]

it looks like this isn't being imported anywhere in the product bundle. I'm stumped as to why this actually works on the docs site, though. 🤔

Great catch! I think it's because the TimelineItem styles get currently added to the docs through styleguide.css.

Anyways, I added the import to "product" 74d0495.

[shawnbot]

Thanks for the fix, @simurai!