lightningd: change msatoshi args to amount_msat.

This is consistent with our output changes, and increases consistency.
It also keeps future sanity checks happy, that we only use JSON msat
helpers with '_msat' fields.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Changed: JSON-RPC: `invoice`, `sendonion`, `sendpay`, `pay`, `keysend`, `fetchinvoice`, `sendinvoice`: `msatoshi` argument is now called `amount_msat` to match other fields.
Changelog-Deprecated: JSON-RPC: `invoice`, `sendonion`, `sendpay`, `pay`, `keysend`, `fetchinvoice`, `sendinvoice` `msatoshi` (use `amount_msat`)

doc/schemas/getroute.request.json

@@ -3,7 +3,7 @@
   "type": "object",
   "required": [
     "id",
-    "msatoshi",
+    "amount_msat",
     "riskfactor"
   ],
   "properties": {
@@ -11,7 +11,7 @@
       "type": "pubkey",
       "description": ""
     },
-    "msatoshi": {
+    "amount_msat": {
       "type": "msat",
       "description": ""
     },

doc/schemas/invoice.request.json

@@ -3,12 +3,12 @@
   "type": "object",
   "additionalProperties": false,
   "required": [
-    "msatoshi",
+    "amount_msat",
     "label",
     "description"
   ],
   "properties": {
-    "msatoshi": {
+    "amount_msat": {
       "type": "msat_or_any",
       "description": ""
     },

doc/schemas/keysend.request.json

@@ -4,13 +4,13 @@
   "additionalProperties": false,
   "required": [
     "destination",
-    "msatoshi"
+    "amount_msat"
   ],
   "properties": {
     "destination": {
       "type": "pubkey"
     },
-    "msatoshi": {
+    "amount_msat": {
       "type": "msat"
     },
     "label": {

doc/schemas/pay.request.json

@@ -9,7 +9,7 @@
     "bolt11": {
       "type": "string"
     },
-    "msatoshi": {
+    "amount_msat": {
       "type": "msat"
     },
     "label": {

doc/schemas/sendonion.request.json

@@ -48,7 +48,7 @@
     "bolt11": {
       "type": "string"
     },
-    "msatoshi": {
+    "amount_msat": {
       "type": "msat"
     },
     "destination": {

doc/schemas/sendpay.request.json

@@ -12,15 +12,17 @@
       "items": {
         "type": "object",
         "required": [
-          "msatoshi",
           "id",
           "delay",
           "channel"
         ],
         "properties": {
-          "msatoshi": {
+          "amount_msat": {
             "type": "msat"
           },
+          "msatoshi": {
+            "deprecated": "true"
+          },
           "id": {
             "type": "pubkey"
           },
@@ -39,7 +41,7 @@
     "label": {
       "type": "string"
     },
-    "msatoshi": {
+    "amount_msat": {
       "type": "msat"
     },
     "bolt11": {