Unable to change stream routing after using Input Setup Wizard to route newly created input messages to stream

When using the new "Input Setup Wizard" workflow to create an input, you have the option to route all messages from the input to either an existing or newly created stream.

Graylog then uses an immutable pipeline that has pipeline rules that perform the routing.

However, users are unable to alter this routing in any way.

The only way I've been able to figure out to remove the routing is to delete the input.

## Expected Behavior

Users have the flexibility to alter stream routing created by Input Setup Wizard.

Consider the following scenarios:
* user wants to route messages from the input to a different stream
* user wants to remove routing to the configured stream and instead route to default stream

## Current Behavior

Users unable to alter stream routing created by the Input Setup Wizard

## Possible Solution

Expose the stream routing as part of the input's configuration page or somewhere else tied to or associated to the input on the inputs page.

## Steps to Reproduce (for bugs)

1. Create a new input
2. Setup Input
3. Choose either `Create Stream` or `Select Stream`

## Context

Customer asking about how this workflow behaves.

## Your Environment

* Graylog Version: 6.3.2
* Java Version: Bundled
* OpenSearch Version: OpenSearch 2.19.3
* MongoDB Version: 6.0.25
* Operating System: Ubuntu Server 22.04 LTS
* Browser version: Google Chrome Version 139.0.7258.128 (Official Build) (arm64)

Feel free to change this to a feature request. I understand that from a coding perspective this is technically working as designed (coded). From a user perspective though, i would consider this a bug.

## Checklist
[] This issue fix need to be backported.
[] Does this issue have **security** implications?