Rename directories to site and library

[taysea]

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What does this PR do?

NOTE: The Netlify deploy process is still configured with aries-site, so when we're ready I can change to site.

• Replaced all innstances of aries-core with library
• Replaced all instances of aries-site with site
• Updated README

Where should the reviewer start?

What testing has been done on this PR?

In addition to the feature you are implementing, have you checked the following:

General UX Checks

• Small, medium, and large screen sizes
• Cross-browsers (FireFox, Chrome, and Safari)
• Light & dark modes
• All hyperlinks route properly

Accessibility Checks

• Keyboard interactions
• Screen reader experience
• Run WAVE accessibility plugin (Chrome)

Code Quality Checks

• Console is free of warnings and errors
• Passes E2E commit checks
• Visual snapshots are reasonable

How should this be manually tested?

Any background context you want to provide?

What are the relevant issues?

Closes #3399

Screenshots (if appropriate)

Should this PR be mentioned in Design System updates?

Is this change backwards compatible or is it a breaking change?