Production Deploy: Pin deploy user to circleci

[davidsmejia]

This pull request updates the deployment workflow to distinguish between the identity used for Terraform resources and the user who actually triggered the deployment. The changes ensure that the Terraform stack identity remains consistent across deployments, while the Slack notification correctly attributes the deploy to the triggering user.

Deployment environment variable changes:

• The DEPLOY_USER environment variable is now hardcoded as circleci in both the deploy and deploy_hotfix jobs to maintain consistent Terraform stack naming and state management. [1] [2]
• A new environment variable, DEPLOY_NOTIFIER, is introduced to capture the actual user who triggered the deployment (github.actor). This value is now used in Slack notifications. [1] [2]

Slack notification update:

• The Slack deployment message in .github/scripts/slackpost_deploy.sh now uses DEPLOY_NOTIFIER instead of DEPLOY_USER to correctly display the deploy triggerer.