feature: Adds corretto-21 repo

[bric3]

At this time I haven't seen public release on the repo, only pre-releases, but given all repo work that way, I'm sure at some point the pre-release (which was the candidate) will eventually be marked a published.

https://github.com/corretto/corretto-21/releases/tag/21.0.0.35.1

https://github.com/corretto/corretto-downloads/blob/e4a73e49c5fd2b0f1630b39239610884fcf74de3/latest_links/indexmap_with_checksum.json#L1597-L1602

    "21": {
     "pkg": {
      "checksum": "760d89e954093c43907454120eef3c1f",
      "checksum_sha256": "4a877d133a3c2c524947a53f5f031cb87264c18c97c858acb084bbf8bf4e476c",
      "resource": "/downloads/resources/21.0.0.35.1/amazon-corretto-21.0.0.35.1-macosx-aarch64.pkg"
     },