Store ceph secret key in age

This allows a node to mount the ceph FS without any extra ceph
configuration in /etc/ceph.

m/hut/secrets/ceph-user.age

@@ -0,0 +1,11 @@
+age-encryption.org/v1
+-> ssh-ed25519 CAWG4Q 35Ak+Mep9k5KnDLF1ywDbMD4l4mRFg6D0et19tqXxAw
+Wgr+CX4rzrPmUszSidtLAVSvgD80F2dqtd92hGZIFwo
+-> ssh-ed25519 MSF3dg OVFvpkAyWTowtxsafstX31H/hJpNZmnOCbvqMIN0+AQ
+VxjRcQmp+BadEh2y0PB96EeizIl3tTQpVu0CWHmsc1s
+-> ssh-ed25519 HY2yRg MJSQIpre9m0XnojgXuKQ/+hVBZNrZNGZqplwhqicpjI
+CLkE52iqpoqSnbzisNjQgxTfNqKeaRl5ntcw1d+ZDyQ
+-> m$8`De%~-grease '85p}`by
+52zMpprONcawWDDtzHdWNwFoYXErPUnVjhSONbUBpDlqAmJmD1LcAnsU
+--- 0vZOPyXQIMMGTwgFfvm8Sn8O7vjrsjGUEy5m/BASCyc
+<EFBFBD>|<04><><EFBFBD>)<29><><EFBFBD><EFBFBD><EFBFBD>*_<>D<EFBFBD>US`<06><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>r <20>s<EFBFBD><73>N<EFBFBD><4E>[֌^e+A1<><31>G.<2E>#<23><><EFBFBD>m<EFBFBD><6D>W<57> <20>5<0C><><EFBFBD><EFBFBD>(