Add tiny icons for line items

[justinwolfe]

Problem/Feature

For line item rows in the new conversation view design, we needed to add two new icons because (per design) the size of the current icons is not appropriate for use in that context.

So this PR adds those two new icons from @kyliedunkley! 🥳

Note: It was stressed to Kylie that these should be "tiny icons"™. I couldn't find any references to what "tiny icons" means searching in various places and this is the only Icon component I know about (and its size prop is number based rather than small medium large etc), so I assume these go here and maybe that was just some design hazing™, but if I should be putting them somewhere else or doing something different, let me know!

Guidelines

Make sure the pull request:

• [ ] Follows the established folder/file structure
• [ ] Adds unit tests
• [ ] If it is a refactor or change to an existing component, have you verified it won't break existing Cypress tests or have you updated them?
• [ ] Did you verify some accessibility (a11y) basics?
• [ ] Adds/updates stories. Guidelines
• [ ] Adds/updates documentation (ie proptypes) Guidelines
• [ ] Has it been tested in Help Scout's supported browsers?
• [ ] Requests review from designer of the feature
• [ ] Add label (bug? feature?)

[justinwolfe]

💯 will do, thank you!

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