feat: add robots.txt to lamassu-server and lamassu-admin

fix: fail fast on lamassu-server default route access

lib/routes.js

@@ -56,6 +56,15 @@ app.use(nocache())
 app.use(express.json({ limit: '2mb' }))
 app.use(morgan(':method :url :status :response-time ms -- :req[content-length]/:res[content-length] b', { stream: logger.stream }))
 
+app.use('/robots.txt', (req, res) => {
+  res.type('text/plain')
+  res.send("User-agent: *\nDisallow: /")
+})
+
+app.get('/', (req, res) => {
+  res.status(404).json({ error: 'No such route' })
+})
+
 // app /pair and /ca routes
 app.use('/', pairingRoutes)