TF Plan security: Plan artifact in GitHub is not encrypted

[chvima]

Using v 0.4.6. Configuration of digger action - upload-plan-destination: github.

Issue: Plan artifact in Github is accessible to everyone who has read access on the repository (this is not configurable on GitHub). Terraform plan binary file can contain sensitive values and shouldn't be accessible to all users.

Suggestion for solution: Implement encryption of the file before storing it to artifacts. It can be either password protected zip file (that the plan is currently in) or file encryption on top of it.

[chvima]

Closing as this is duplicate of #817