non-admin user cannot create content pack

## Expected Behavior

As a GrayLog user with the `contentpacks:*` permission I can create a content new content pack.

## Current Behavior

As a GrayLog user with the `contentpacks:*` permission, when I attempt to create a new content pack with the web UI I get the error:

```
The permissions check for the following request failed,
while trying to access /system/contentpacks/create.
There was an error fetching a resource: Forbidden. Additional information: Not authorized
```

However, I can view the content pack page and create a new version of an existing content pack. I can then successfully download that content pack, uninstall it, delete it, upload it, and install it again.

The only thing I can't do is create a new content pack.

## Possible Solution

## Steps to Reproduce (for bugs)

1. Create a non-administrative user with broad permissions including `contentpacks:*`
2. Log in as that non-admin user and navigate to `system/contentpacks`
3. Click “Create a Content Pack”. Set Name, Summary, and Vendor to “foo”. Select any trivial object. Click `Next`.
4. Observe the error

Background: I used the "Power User" role, defined as:
```
$ curl http://graylog:9000/api/authz/roles -X GET -H "X-Requested-By: cli" -u admin:AdministratorPassword -sS | jq '.roles[] | select(.name == "Power User")'
```
```json
{
"id": "62bb485f292b91331d5ef92c",
"name": "Power User",
"description": "Power Users can do everything except admin GrayLog itself",
"permissions": [
"clusterconfigentry:read",
"pipeline:*",
"authhttpheaderconfig:read",
"sidecar_collector_configurations:read",
"users:read",
"aws:read",
"journal:read",
"licenseinfos:read",
"eventdefinitions:*",
"systemjobs:read",
"authservicebackend:read",
"dashboards:*",
"sources:read",
"notifications:read",
"collectors:read",
"lookuptables:read",
"searches:*",
"inputs:read",
"loggersmessages:read",
"decorators:*",
"sidecar_collectors:read",
"fieldnames:read",
"contentpack:*",
"eventnotifications:*",
"jvmstats:read",
"throughput:read",
"pipeline_rule:*",
"stream_outputs:*",
"messages:*",
"messagecount:read",
"view:*",
"systemmessages:read",
"indexsets:read",
"streams:*",
"catalog:list",
"outputs:read",
"default-view:set",
"authserviceglobalconfig:read",
"indexercluster:read",
"pipeline_connection:*",
"sidecars:read",
"urlwhitelist:read",
"roles:read",
"deflector:read",
"grantsoverview:read",
"buffers:read",
"indexranges:read",
"system:read",
"indices:read",
"metrics:*",
"loggers:read"
],
"read_only": false
}
```

## Context

Some Graylog non-admin users need to create content packs so they can take their dashboards and pipelines from one graylog instance to another, such as promotion dev to stage to prod or for different geographies.

Discussion started in https://community.graylog.org/t/content-packs-and-permissions/24546

## Your Environment

* Graylog Version: 2.1.3
* Java Version: included
* Elasticsearch Version: included
* MongoDB Version: included
* Operating System: Kubernetes/Helm
* Browser version: Chrome 103