Add yaml document separators to CRDs to make helm show crds valid

[Vasfed]

Modern helm has command show crds to get CRDs from chart without untarring etc:

helm show crds mattermost/mattermost-operator

It concatenates files from crds/, thus currently produces invalid yaml for mattermost-operator (with keys redefinition).

Helm has a proposal to forcefully add separators, but it was not accepted for more than a year at the moment and it's not clear when and if it will be.

This PR makes helm's output valid and useable

[mattermost-build]

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[Vasfed]

/check-cla