fix(server): ensure log entries have level silly (#496)

After recent changes to the logger, child entries only inherit their
parent level if specified.

garden-service/src/server/commands.ts

@@ -71,7 +71,7 @@ export async function resolveRequest(
   const cmdGarden = await Garden.factory(garden.projectRoot, garden.opts)
 
   // We generally don't want actions to log anything in the server.
-  const cmdLog = log.placeholder(LogLevel.silly)
+  const cmdLog = log.placeholder(LogLevel.silly, { preserveLevel: true })
 
   const cmdArgs = mapParams(ctx, request.parameters, command.arguments)
   const cmdOpts = mapParams(ctx, request.parameters, command.options)