feat(forknet): allow running traffic generator with a key map secret (#…

…11375)

we've been using the mirror tool without a secret used to map keys,
which is fine when we're running internal tests. but if we want to start
a forknet instance that will later be opened up to the public, we'll
want to use a mix the mapped keys with a secret. so here we will assume
that it will be placed in ~/.near/setup/mirror-secret.json (or
~/.near/target/setup/mirror-secret.json for V2 setups) and we'll use it
if so

pytest/tests/mocknet/helpers/neard_runner.py

@@ -850,8 +850,12 @@ def start_neard(self, batch_interval_millis=None):
                     self.source_near_home_path(),
                     '--target-home',
                     self.target_near_home_path(),
-                    '--no-secret',
                 ]
+                if os.path.exists(self.setup_path('mirror-secret.json')):
+                    cmd.append('--secret-file')
+                    cmd.append(self.setup_path('mirror-secret.json'))
+                else:
+                    cmd.append('--no-secret')
                 if batch_interval_millis is not None:
                     with open(self.target_near_home_path('mirror-config.json'),
                               'w') as f: