feat: update the channel naming conv

[camilamacedo86]

Description

• Replace preview with candidate for channel naming check.
• Improve channels names statements and descriptions
• Add a note to clarifies the convention motivation

Motivation That was checked that the most appropriated convention name would be candidate instead of preview.

[openshift-ci[bot]]

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This pull-request has been approved by: anik120, camilamacedo86

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