Better UX for custom server - URL validation

[tomasMizera]

Let's add a validation rule when setting up a custom server URL:

• URL must end with / -> or even better, add it automatically if not present
• Add example of how the URL should look like, e.g. https://my-server-app.com/

[jozef-budac]

/ is added automatically on the end and also a sample URL is visible when the input field is empty (on 2024.2.0 RC)