make autosign a config file option

If set in the config file, the option may be overridden on the command
line with --no-autosign

mmgen/cfg.py

@@ -221,6 +221,7 @@ class Config(Lockable):
 	force_standalone_scrypt_module = False
 	enable_erigon                  = False
 	autochg_ignore_labels          = False
+	autosign                       = False
 
 	# regtest:
 	bob          = False
@@ -287,6 +288,7 @@ class Config(Lockable):
 	# coin-specific only:  bch_cashaddr (alias of cashaddr)
 	_cfg_file_opts = (
 		'autochg_ignore_labels',
+		'autosign',
 		'color',
 		'daemon_data_dir',
 		'debug',

mmgen/data/mmgen.cfg

@@ -85,6 +85,10 @@
 # variants (see below):
 # tw_name my-other-tracking-wallet
 
+# Uncomment to make autosign with automount the default.  Can be overridden
+# on the command line with --no-autosign
+# autosign true
+
 #####################################################################
 ## RPC options. These also have coin-specific variants (see below) ##
 #####################################################################