feat: preview-create becomes preview-deploy to allow updating of prev…

[gary-ix]

…iew environments rather than always creating new ones

Problem

Currently --preview-create only creates new preview deployments and does not allow for updating a preview deployment.

Solution

Replaced --preview-create with --preview-deploy:

• If preview deployment exists it pushes changes to that preview.
• If preview deployment does not exist it creates the preview deployment.

Implementation

• Added checkPreviewDeploymentExists() function
• Routes to appropriate deployment function based on existence
• Adds deprecation for --preview-create

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