feat: Deploy preview with details which data is going to be updated for each file changed (similar to terraform plan command)

What problem does this feature solve?

Before deploying changes to the cloud, it’s beneficial to preview what changes will be submitted. This is similar to the terraform plan command.

While there is a preview flag for npx checkly deploy -p, it only provides a list of logicalIds without showing the exact content of the changes. Without these details, it becomes difficult to understand what will be updated in the cloud, as demonstrated in the image below:

Ideally, a standalone command like npx checkly preview would be available for previews, similar to:

terraform plan
cdk diff
pulumi preview

How would you implement this feature?

Proposed Implementation Steps:

1. Retrieve the current data from the server via API.

2. Gather the data to be sent to the API.

3. Compare the differences and display them in the CLI in a format that clearly shows the current values and the proposed updates for easy understanding.

Start by examining the existing npx checkly deploy -p preview path, then trace how current data is retrieved from the server and how deployment data is gathered for the API. The work is done when a preview command clearly displays current values and proposed updates for each changed file or resource.