RHCOS multi-arch builder splunkforwarder container fails to build

[marmijo]

The splunkfowarder container on the RHCOS multi-arch builders has been failing to build due to multiple reasons. Mainly because the internal gitlab repos being used are outdated and the version of the splunkforwarder package being installed is no longer available in the internal repos.

No match for argument: splunkforwarder-8.2.6
Error: Unable to find a match: splunkforwarder-8.2.6

We should stop building the base splunkforwarder image on the remote builders and instead just pull the image provided by IT, which has the newer splunk package already installed.

See: https://issues.redhat.com/browse/COS-2966

[dustymabe]

+1

[marmijo]

PR to update the butane config for the multi-arch builders to stop building the ITPAAS base splunkforwarder container and build only the splunk sidecar container: #1045