Update Support URL in README on Extension repo

[mapachurro]

Description

The old URL contained the zendesk format, which has been out of date, but functional, for a long time. It no longer resolves to the correct, live site, and will soon break.

Related issues

This is the first fix in a very large amount of fixes that will have to the MetaMask multicodeverse, likely meaning we create an npm package to convert URLs to variables and maintain them in a sane way.

Manual testing steps

Go to metamask.zendesk.com

• The content is out of date, and it's not the correct site
• The correct site is at support.metamask.io, and the content is up to date (as much as possible <3 )

Screenshots/Recordings

Before

After

Pre-merge author checklist

• [x] I’ve followed MetaMask Coding Standards.
• [x] I've completed the PR template to the best of my ability
• [x] I’ve included tests if applicable
• [x] I’ve documented my code using JSDoc format if applicable
• [x] I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• [ ] I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• [ ] I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions[bot]]

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