CLI Cloud commands: make stack info mandatory

[AgnesToulet]

Feature Description

The new stack option added to the Cloud configuration in #5420 should become as mandatory as the token information. If it's not provided, the command should fail.

It can be specified in different ways:

• When running the k6 cloud login command with the --stack parameter or using the interactive mode (in this case, this should be the stack slug or full URL)
• In the script options, adding the stackID option
• In the env variables, using the K6_CLOUD_STACK_ID env variable

It would be nice to make the different options a bit more consistent and either use the stack slug everywhere, or support stack slug/url/id everywhere.

Suggested Solution (optional)

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Already existing or connected issues / PRs (optional)

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