Docs - Add obsolete package info to troubleshooting

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What does this MR do?

Some customers experience an issue with switching from EE to CE or vice versa. The issue is that yum doesn't treat a local rpm file the same way as it treats a repo package install. For some reason, the obsoletion checks will actually prevent the rpm install unless you tell it not to or just use rpm instead. This MR adds a blurb about to the troubleshooting section to document that problem.