listconfigs: show plugin options in 'configs' with normal options.

This integrates them with configvars properly: they almost "just work"
in listconfigs now, and we don't put them in a special sub-object
under their plugin.

Unfortunately, this means `listconfigs` now has a loose schema: any
plugin can add something to it.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: Plugins: reloaded plugins get passed any vars from configuration files.
Changelog-Deprecated: Config: boolean plugin options set to `1` or `0` (use `true` and `false` like non-plugin options).

plugins/fetchinvoice.c

@@ -1617,7 +1617,7 @@ static const char *init(struct plugin *p, const char *buf UNUSED,
 
 	rpc_scan(p, "listconfigs",
 		 take(json_out_obj(NULL, "config", "experimental-offers")),
-		 "{experimental-offers:%}",
+		 "{configs:{experimental-offers:{set:%}}}",
 		 JSON_SCAN(json_to_bool, &exp_offers));
 
 	if (!exp_offers)

plugins/offers.c

@@ -1050,7 +1050,9 @@ static const char *init(struct plugin *p,
 
 	rpc_scan(p, "listconfigs",
 		 take(json_out_obj(NULL, NULL, NULL)),
-		 "{cltv-final:%,experimental-offers:%}",
+		 "{configs:"
+		 "{cltv-final:{value_int:%},"
+		 "experimental-offers:{set:%}}}",
 		 JSON_SCAN(json_to_u16, &cltv_final),
 		 JSON_SCAN(json_to_bool, &offers_enabled));
 

plugins/pay.c

@@ -582,7 +582,9 @@ static const char *init(struct plugin *p,
 
 	rpc_scan(p, "listconfigs",
 		 take(json_out_obj(NULL, NULL, NULL)),
-		 "{max-locktime-blocks:%,experimental-offers:%}",
+		 "{configs:"
+		 "{max-locktime-blocks:{value_int:%},"
+		 "experimental-offers:{set:%}}}",
 		 JSON_SCAN(json_to_number, &maxdelay_default),
 		 JSON_SCAN(json_to_bool, &exp_offers));