LookupServer: Watch /etc/hosts for changes during runtime

This adds a FileWatcher to the LookupServer which watches '/etc/hosts'
for changes during runtime and reloads its contents. If the file is
deleted, m_etc_hosts will be cleared.

Since we now need to access '/etc/hosts' later during runtime, it needs
to be unveiled with read permissions.

Userland/Services/LookupServer/main.cpp

@@ -30,6 +30,11 @@ int main([[maybe_unused]] int argc, [[maybe_unused]] char** argv)
         return 1;
     }
 
+    if (unveil("/etc/hosts", "r") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
     if (unveil(nullptr, nullptr) < 0) {
         perror("unveil");
         return 1;