Add loadwallet and createwallet RPC load_on_startup options

This maintains a persistent list of wallets stored in settings that will
automatically be loaded on startup. Being able to load a wallet automatically
on startup will be more useful in the GUI when the option to create wallets is
added in #15006, but it's reasonable to expose this feature by RPC as well.

test/functional/test_runner.py

@@ -243,6 +243,7 @@ BASE_SCRIPTS = [
     'p2p_node_network_limited.py',
     'p2p_permissions.py',
     'feature_blocksdir.py',
+    'wallet_startup.py',
     'feature_config_args.py',
     'feature_settings.py',
     'rpc_getdescriptorinfo.py',