mounts: take an SMB source's username as a setting and its password as its own secret, and wait for them

The one INI secret smb-credentials could not be given through the desk
prompt, which takes one hidden line, and a missing login was said as a
fault: the first-node gate put the build back and the operator was told
nothing was theirs to do. The username is now the setting smb-users and
each password the one-line secret smb-password-<source>; a source missing
either answers waits through mesh-sdk's health answer (hq ADR 0283,
issue 386, issue 379).

modules/mounts/module.json

@@ -48,12 +48,16 @@
       "kind": "preference",
       "default": "none",
       "why": "a machine has no occasional source until its assignment names one: space-separated name=smb://<host>/<share>@<mountpoint> or name=disk:<uuid>@<mountpoint>, each optionally :ro (hq ADR 0263 rule 6)"
+    },
+    "smb-users": {
+      "kind": "preference",
+      "default": "none",
+      "why": "the username each SMB source logs in with: space-separated name=username; not a secret, so a setting, beside each source's password in its own secret smb-password-<source> (hq ADR 0283)"
     }
   },
   "own-secrets": {
-    "smb-credentials": {
-      "path": "${dir:state}/smb-credentials.secret",
-      "taken": "at-start",
+    "smb-password-*": {
+      "path": "${dir:state}/smb-password-*.secret",
       "issued-by": "outside"
     }
   },
@@ -85,7 +89,7 @@
       "type": "file",
       "path": "/etc/mesh-mounts/mounts.conf",
       "mode": "0644",
-      "content": "# Written by the mesh (module mounts, novox/hq ADR 0263) from this machine's assignment: the settings\n# shares and sources, and the binding of nfs-share. Replaced on every push; change the settings, not this.\n# The module's process reads it as root every 30 seconds and writes one .mount and .automount per entry.\nshares=${setting:shares}\nsources=${setting:sources}\nserver=${bound:nfs-share:from}\nat=${bound:nfs-share:at}\naccount=${machine:account}\nnode=${machine:name}\nsecret=${dir:state}/smb-credentials.secret\nstate=${dir:state}\n"
+      "content": "# Written by the mesh (module mounts, novox/hq ADR 0263) from this machine's assignment: the settings\n# shares, sources and smb-users, and the binding of nfs-share. Replaced on every push; change the settings, not this.\n# The module's process reads it as root every 30 seconds and writes one .mount and .automount per entry.\nshares=${setting:shares}\nsources=${setting:sources}\nsmb-users=${setting:smb-users}\nserver=${bound:nfs-share:from}\nat=${bound:nfs-share:at}\naccount=${machine:account}\nnode=${machine:name}\npasswords=${dir:state}\nstate=${dir:state}\n"
     },
     {
       "id": "bus-dir-parent",