Update Cloudflare Logpush dashboards pack for Graylog 4.0

The [Cloudflare Logpush content pack](https://github.com/Graylog2/graylog-s3-lambda/blob/master/content-packs/cloudflare/cloudflare-logpush-content-pack.json) was originally created with Graylog 3.x and appears to need some updates for optimal functionality in the newly released Graylog 4.0.

This content pack includes several dashboards, which appear to still mostly work correctly in Graylog 4.0 from a quick test:
* Cloudflare - Bots Converted Dashboard
* Cloudflare - Performance Converted Dashboard
* Cloudflare - Reliability Converted Dashboard
* Cloudflare - Security Converted Dashboard
* Cloudflare - Snapshot

I found one small issue when testing:

The counts at the top of the Cloudflare - Performance dashboard no longer show after installation. This is probably because the dashboards were created with an old version of Dashboards, which was completely separate from search. Now, the widget sizing has changed slightly, which probably resulted in the hidden numbers.

It looks like the size of the widgets need to be increased, like this:

See the Cloudflare docs for an example of what the Dashboards look like:
https://developers.cloudflare.com/logs/analytics-integrations/graylog

Also, the [gelf-sample-data](https://github.com/danotorrey/gelf-sample-data/blob/master/src/main/java/com/dantorrey/Main.java) tool which I threw together quickly, can be used as a start to generate sample Cloudflare sample logs to test the dashboards.