refactor(ops): Move Nix cache secret to agenix

... and also the public key, just to keep the distribution mechanism
the same.

Change-Id: Ief14daf9344c0fb99eeb5789c1ec9bfb1f12bee0

ops/secrets/nix-cache-priv.age

@@ -0,0 +1,11 @@
+age-encryption.org/v1
+-> ssh-ed25519 dcsaLw GSjmDlPaOHw2uNxaGgQ/Jvt1xyL6pqnAGOhW/PXq0g0
+Lw27V3JPG6iBGiHpnHEm1B07skTYkYZHkCtDbRVXj/4
+-> ssh-ed25519 CpJBgQ Y52Trw6EsiR5xfVMB7bh8vLPnNlNj9RKu2WYVKOd9SQ
+51egTYyWQj+HUVytA1Te0kcJCeKQn3GkW0ZODGPylOI
+-> ssh-ed25519 OkGqLg rU7V7ekAJ/7IxnbP5mbXT9fCH3zYlzDajkbzStACfmM
+l0CIZ2kIod05a2mWeFTM5BAcfXp3VNqsfLzjknXv6d0
+-> C#9J-grease 6
+uBB/nrNzeiZBynmHdla48aU6JC45+8T2WLQ
+--- MG+HoZ+OIMOSBp0IZqamiW4ShQZF9o8XDRIRUBYXY3E
+	§ùÝàWG,PÂjžã 'f<14>â¯?vÁÎÀ3Y´1ÏC-¥‚´+“³‰_eõѸý1JA«6ô]4µÞÒaB‘ž+ϾšÏ¼Ð9ɪ…ƒÓXòs2ép›àZ!<21>ÈtMÏ)j\<!§gïØA9ì*Wj€†®Ž×D6ò+kÞ

ops/secrets/nix-cache-pub.age

@@ -0,0 +1,12 @@
+age-encryption.org/v1
+-> ssh-ed25519 dcsaLw TL5QToF0mDivu98x9gXaSl69LUZL5iKBRqabHAdVWzM
+UajZlNzYwlyol2mgUFMieb2u/9B+0guhU/lAadDdwZI
+-> ssh-ed25519 CpJBgQ 7S+W2LgW2ZqUVb3c7Yk0LevWX3sWMm57yLC5Xqoxowo
+jjN6v+kZ22Y1QZF92JXkonPTa/AwlVGK5Tfx6t6O02k
+-> ssh-ed25519 OkGqLg hr9WfRaMD8ItNpy5MUse6h1XWvsfTVGlKhy9EfJenjE
+hKcAGPH2F+tjirBZLn2UfoOkFzBj0jAz11MuBmR+Ruc
+-> _IV%wdMT-grease sj}ltN 2j: , `
+32ynfXOvS7JtSNvxhEDJq9UntSBcmh7VLIBSGmzNlv9QrcjtLluFy0ig2jYuYVUh
+bT1LncUASkgCxW6GPqd21oYOn4ygDvZqTgi+FB6O
+--- fUjoaFfrtbi4tV6zqH3t9wlY+8TDwcLbV6WWlzQqnJY
+sI»ó;!Öït¨UÁÙtUKiƒQ<C692>õ¤ë
êÒaµ]…|ã×ÉŽìýN@<40>yŠ‚dÙçžÕŒu%zµçfJÝ0F!ã÷ȽXjs¹5Få!ðOÛõÌ<C3B5>û‰³ ŠŽ

ops/secrets/secrets.nix

@@ -20,5 +20,7 @@ in {
   "gerrit-queue.age" = default;
   "grafana.age" = default;
   "irccat.age" = default;
+  "nix-cache-priv.age" = default;
+  "nix-cache-pub.age" = default;
   "owothia.age" = default;
 }