lnrpc+lncli: deprecate sat_per_byte and add sat_per_vbyte

This commit deprecates/replaces the old field `sat_per_byte` with
`sat_per_vbyte`. While the old field suggests sat per byte, it’s
actually using sat per virtual byte. We use the Hidden param to hide all
the deprecated flags. These flags won't show up in help menu onwards,
while stay valid that can be passed from cli. Thus bash scripts
referencing these fields won't be broken.

lnrpc/wtclientrpc/wtclient.swagger.json

@@ -289,6 +289,11 @@
           "description": "The maximum number of updates each session we negotiate with watchtowers\nshould allow."
         },
         "sweep_sat_per_byte": {
+          "type": "integer",
+          "format": "int64",
+          "description": "Deprecated, use sweep_sat_per_vbyte.\nThe fee rate, in satoshis per vbyte, that will be used by watchtowers for\njustice transactions in response to channel breaches."
+        },
+        "sweep_sat_per_vbyte": {
           "type": "integer",
           "format": "int64",
           "description": "The fee rate, in satoshis per vbyte, that will be used by watchtowers for\njustice transactions in response to channel breaches."
@@ -390,6 +395,11 @@
           "description": "The maximum number of backups allowed by the watchtower session."
         },
         "sweep_sat_per_byte": {
+          "type": "integer",
+          "format": "int64",
+          "description": "Deprecated, use sweep_sat_per_vbyte.\nThe fee rate, in satoshis per vbyte, that will be used by the watchtower for\nthe justice transaction in the event of a channel breach."
+        },
+        "sweep_sat_per_vbyte": {
           "type": "integer",
           "format": "int64",
           "description": "The fee rate, in satoshis per vbyte, that will be used by the watchtower for\nthe justice transaction in the event of a channel breach."