Consider returning command results as a JSON string

[ericglau]

Currently the commands return results in plain text.

Examples:

• deploy prints Deployed to address: ...
• proposeUpgrade prints Proposal ID: ... and Proposal URL: ...
• getDeployApprovalProcess and getUpgradeApprovalProcess print Approval process ID: and Via: ... (if via it is not undefined)

Since this CLI is mainly consumed programmatically, for example from the Foundry Upgrades plugin, we should consider making these results more consumable by printing JSON strings instead.

Particularly, it would also allow for some returned fields to be undefined, for example the via field from the approval process.

This would be a breaking change and it is why the current version of this CLI is still tagged as alpha.