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The old URL contained the zendesk format, which has been out of date, but functional, for a long time.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• The content is out of date, and it's not the correct site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.

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This PR has been automatically marked as stale because it has not had recent activity in the last 60 days. It will be closed in 14 days. Thank you for your contributions.

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This PR was closed because there has been no follow up activity in the last 14 days. Thank you for your contributions.