add btrbk system snapshots

secrets/btrbk-keyfile.age

@@ -0,0 +1,11 @@
+age-encryption.org/v1
+-> ssh-ed25519 Gc/MTQ kKd7HFgJtplJohdcYXwFM+UXZBwBoQ9KJwfQ2jxS2g4
+yrNEIKJYffcf/NG5XnWl1Icic/gUWVsDK1ddqC+QWI0
+-> ssh-ed25519 mOIk4w /3/0Mb4pFu7a/480skeucHFoAddr08h89qqL7Ojt/gA
+SaXfyGJFDBTzU+zkDxVLe4SK6UNd9/6g3qtXYOQ/Wwo
+-> ssh-ed25519 l9wOAw 8wgspVkjHpxD2tzpVD0yZvipthOVWA6mUWVaWY3Ls20
+iSFw5EEGiv4uYw2JSv8T0fWajLBCajWKQYAHzvjOEwk
+--- +3nHDKkQ7xsKKk8wLBe6/Y5aSm8E25+7XlxrfB6V72g
+<03>><3E><><EFBFBD>F<EFBFBD>㿫<EFBFBD>s<EFBFBD>,F<>)<29><><EFBFBD>X<EFBFBD><58><EFBFBD>><3E>~_<><5F>
+;W<>0<EFBFBD>j<13>><3E><><EFBFBD><EFBFBD><EFBFBD>g*<2A><03><>ԃ<>!%<25>%`w<>;<3B><><EFBFBD>R<EFBFBD><52>w<1A><><EFBFBD>J1K͵̨R|sAB`<60>([
+<1E>~d<><64><EFBFBD><EFBFBD>XM<58><4D><EFBFBD>\<5C><>lo<6C><0F>>F<>
ķ<>H<12><><EFBFBD><EFBFBD>

secrets/secrets.nix

@@ -7,4 +7,5 @@ let
 in
 {
   "k3s.age".publicKeys = keys;
+  "btrbk-keyfile.age".publicKeys = keys;
 }