feat: add Dub plugin

[bensabic]

Summary

Adds Dub plugin with the following actions:

• Create Link: Create a new short link
• Upsert Link: Create or update a link by URL or external ID

Features:

• Grouped config fields for Link IDs, Link Preview, and UTM Parameters
• Returns link ID, short URL, QR code URL, domain, key, and destination URL

Test plan

• Connection test validates credentials
• Actions execute successfully in a workflow
• Error handling works for invalid inputs

[vercel]

@bensabic is attempting to deploy a commit to the Vercel Labs Team on Vercel.

A member of the Team first needs to authorize it.