When creating an input, have graylog show a note if the selected port is already in use

## What?

Its not uncommon to create multiple of the same input type. For example to more easily delineate logs from different sources our types of sources, one may have multiple syslog inputs. In doing this, the default port is populated in the port input box, and should the user forgot (or not be aware that they need to) change this, they input will fail to start and show an error (expected, thats ok and normal).

My thinking was that graylog already knows (via mongo) what inputs exist and can use this to help provide hints to users to save them some time and some trouble. Another way this can be useful is that once you are in the workflow of creating a new input, you can no longer use that page to see what ports are already in use. It would save time to be able to see "oh this port is in use let me choose another".

Crude mockup:


## Why?

To help reduce friction for creating inputs and make this process more easy and more user frieindly.

## Your Environment

* Graylog Version: 5.1.3
* OpenSearch Version: 2.8.0
* MongoDB Version: 6.0.7
* Operating System: Ubuntu Server 22.04 LTS
* Browser version: Google Chrome Version 114.0.5735.198 (Official Build) (arm64)

Let me know if there are any questions!