Add ferrad.as to sites.yml

[cesarferradas]

Website (if applicable): https://ferrad.as

This PR is:

• [x] Adding a new domain
• [ ] Updating existing domain
• [ ] Changing domain name
• [ ] Removing existing domain from list
• [ ] Website code changes (darktheme.club site)
• [ ] Other not listed

• [x] The following information is filled identical to the data file

I confirm that I have read the FAQ page, particularly the red section about inappropriate content, and I attest that this site is appropriate based on those criteria.

• [x] Check to confirm

- domain: ferrad.as
  url: https://ferrad.as/
  method: mediaquery
  last_checked: 2023-06-04

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[garritfra]

Thanks!