feat: Added support for Staging Distribution

[ogugu9]

Description

• Support for staging distribution feature.
  • add staging variable
  • add continuous_deployment_policy_id variable

Closes #131

Motivation and Context

In order to use staging distribution feature, we must set staging = true to the staging distribution and specify continuous_deployment_policy_id for the primary distribution.
So I added these variables.

Breaking Changes

No breaking changes.

How Has This Been Tested?

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects

• I have executed pre-commit run -a on my pull request

❯ pre-commit run -a 
Terraform fmt............................................................Passed
Terraform wrapper with for_each in module................................Passed
Terraform validate.......................................................Passed
Terraform docs...........................................................Passed
Terraform validate with tflint...........................................Passed
check for merge conflicts................................................Passed
fix end of files.........................................................Passed

[antonbabenko]

This PR is included in version 3.3.0 🎉

[github-actions]

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