secrets: migrate to agenix

It is finally time to graduate to an actually secure, stateless
solution.

secrets/wireguard/.gitattributes

@@ -1 +1,2 @@
 /default.nix filter diff
+public-key.txt filter diff

secrets/wireguard/porthos/private-key.age

@@ -0,0 +1,10 @@
+age-encryption.org/v1
+-> ssh-ed25519 cKojmg +WwRpd2MzycutQFXyLsr2+GzSgF67Z6UuvyqYZaLd3w
+sppt8HzaZP3yxnvnhzjl18Trnz8g3VyXJ6CaVBWd7jA
+-> ssh-ed25519 jPowng wanoqGB7T8bim/WZ4IAYViFQoGzaIZSgeoTr3YKpeTY
+ihDAdGa1XVW/qQz40V1v7a7iK7tu0EHMa7ayIogpcRw
+-> l-grease |PIcZ NIr >0;*
+4o8o0bevQZ6uDSx1WxxlDCURbFCM+yK1XPdrb9aztCSvG2a+ne78E42l5rBcoH7I
+m51A8uWS4nSj36N/76v6K4kelxKzWUg
+--- O6cGbTAVbDcdmPHf7UzfZiyiRtu1yfL4sBI+CkJA1qw
+ý
qýŐ$ň`żw'čS“X¸]Ąá÷ř®úî…?¤6‹Đ/ĆN(Bžň N«a”.˙ HŽ7żí•I<E280A2>ú÷Ŕoz‡/4:sK",7J

secrets/wireguard/richelieu/private-key.age

@@ -0,0 +1,10 @@
+age-encryption.org/v1
+-> ssh-ed25519 cKojmg rYhrpoTaFjLBGtbCXxEK7jZa+KnriEV/kWViIEjmuQs
+jHMSjxKIIqjUnpAcEo3JgsieI1iiA5/gKEx8+QFhDgY
+-> ssh-ed25519 jPowng 6sQQFvSbWdjgDYSKmJ/CBG+BTzxFghX4SaJ4GyACKWc
+OABJuh+Ta8q+G0onF/9bz3xxv4zTlHYlF4AjC5P6Y6I
+-> xwW|#D`-grease $xYH C m8lBk9
+OBqgvLNIurE0qNaSB7dO2/6dQkVXeLgf/3l9gGlRJ6ynhqwmbXOUa0vyj+OBz27O
+uI97+0y1TFAs3HN0Y8nj8LrwsafbDENu99JuVow2OuLKeSqc7sxOQQ
+--- 9filSHStPTJJGDLY7AWzIXu/6tK4X0okT522sc4OJTc
+M{ｲ顗仭$ｹ:Nﾙ災[ﾝｶｬ2xy8&腴_{RﾜLX<4C>W√€<E2889A>ｻxﾑ*Pr`ｾUｲp<EFBDB2>Jﾉ枇鵲#藝ﾔ<E8979D>ﾗ<EFBFBD>覬粘	s