chore: Check port availability before starting Tomcat (#2716)

It gave just a cryptic error before, hard to determine what to do.

Closes #2648.

Co-authored-by: StaNov <[email protected]>

backend/app/src/main/kotlin/io/tolgee/configuration/PortAvailability.kt

@@ -0,0 +1,43 @@
+package io.tolgee.configuration
+
+import okhttp3.internal.closeQuietly
+import org.slf4j.LoggerFactory
+import org.springframework.beans.factory.annotation.Value
+import org.springframework.boot.web.servlet.ServletContextInitializer
+import org.springframework.context.annotation.Bean
+import org.springframework.context.annotation.Configuration
+import java.io.IOException
+import java.net.ServerSocket
+import kotlin.system.exitProcess
+
+@Configuration
+class PortAvailability {
+  private val logger = LoggerFactory.getLogger(PortAvailability::class.java)
+
+  @Bean
+  fun portAvailabilityChecker(
+    @Value("\${server.port:8080}") port: Int,
+    @Value("\${management.server.port:#{null}}") managementPort: Int?,
+  ): ServletContextInitializer {
+    return ServletContextInitializer {
+      checkPortAvailability(port, "server.port")
+      managementPort?.also { checkPortAvailability(it, "management.server.port") }
+    }
+  }
+
+  private fun checkPortAvailability(
+    port: Int,
+    propertyKey: String,
+  ) {
+    try {
+      ServerSocket(port).closeQuietly()
+    } catch (e: IOException) {
+      logger.error(
+        "Port $port is already in use. " +
+          "Please free the port or specify a different port using the `$propertyKey` property.",
+        e,
+      )
+      exitProcess(1)
+    }
+  }
+}