hsmd: add hsmd_preapprove_keysend and check_preapprovekeysend pay modifier

Changelog-added: hsmd: A new message `hsmd_preapprove_keysend` is added.
Changelog-added: JSON-RPC: A new command `preapprovekeysend` is added.

doc/schemas/preapproveinvoice.request.json

@@ -7,7 +7,8 @@
   ],
   "properties": {
     "bolt11": {
-      "type": "string"
+      "type": "string",
+      "added": "v23.02"
     }
   }
 }

doc/schemas/preapprovekeysend.request.json

@@ -0,0 +1,27 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [
+    "destination",
+    "payment_hash",
+    "amount_msat"
+  ],
+  "properties": {
+    "destination": {
+      "type": "pubkey",
+      "added": "v23.02"
+    },
+    "payment_hash": {
+      "type": "hex",
+      "added": "v23.02",
+      "description": "the hash of the *payment_preimage* which will prove payment",
+      "maxLength": 64,
+      "minLength": 64
+    },
+    "amount_msat": {
+      "type": "msat",
+      "added": "v23.02"
+    }
+  }
+}

doc/schemas/preapprovekeysend.schema.json

@@ -0,0 +1,6 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "type": "object",
+  "additionalProperties": false,
+  "properties": {}
+}