Added intro text

Suzanne Selhornrequested to merge
sselhorn-master-patch-62158 into master

Took intro text from this page: https://docs.gitlab.com/ee/install/cloud_native/ And pasted it here. I'm going to remove that other page and bring the Operator and Helm chart pages one level to the left.

Related to: gitlab-org/technical-writing#642

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