[Icon] Add dynamic source connect icon

[Rusty-UX]

Adds support for dynamic source connect icon

• This icon is used when a dynamic source is connected, and powering part of the experience: either data, or functionality.
• This icon is used in context of Shopify Admin, and Shopify Mobile for merchandising flows.

WHY are these changes introduced?

• Provides additional specificity in how we communicate dynamic source connections in admin and online store

WHAT is this pull request doing?

• Adds support for dynamic source connect icon
• Updates description for add dynamic source icon

How to 🎩

🖥 Local development instructions
🗒 General tophatting guidelines
📄 Changelog guidelines

🎩 checklist

• Tested a snapshot
• Tested on mobile
• Tested on multiple browsers
• Tested for accessibility
• Updated the component's README.md with documentation changes
• Tophatted documentation changes in the style guide

[kyledurand]

@Rusty-UX I think tests are failing because this icon has some unwanted svg attribute bloat.

Can you try:

1. cd polaris-icons
2. yarn optimize
3. Then push up the changes?

If that's still failing let me know and I'll take another look