Cannot add more than a single Parameter to a content pack

When attempting to create parameters during the "Create content pack" workflow, the `Create parameter` button only allows creating a single parameter. After one parameter is created, clicking `Create parameter` bring up an edit modal.

Please let me know if there are any questions.

## Expected Behavior

More than one parameter can be created.

## Current Behavior

Only a single parameter can be created.

## Possible Solution

## Steps to Reproduce (for bugs)

Via the Graylog Web UI:

1. Navigate to System / Content Packs
2. Create a content pack
3. Input anything for required fields:
* name
* summary
* vendor
* at least one content pack selection (i'm attempting to select an input)
4. Click `Next` on the left column menu
5. Click `Create parameter`
6. Fill in required fields
* Title
* Name
* Description
7. Click `Create parameter` to create a second parameter

## Context

## Your Environment

* Graylog Version: 6.3.3

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