ci: pin DEPLOY_USER to circleci; add DEPLOY_NOTIFIER for Slack

[davidsmejia]

Issue Number

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Purpose/Implementation Notes

This pull request updates the deployment workflow to better distinguish between the identity used for Terraform deployments and the user who actually triggered the deployment. The main improvements are to environment variable handling and Slack notification messaging.

Workflow environment variable changes:

• DEPLOY_USER is now always set to circleci to ensure Terraform stacks remain consistent and do not fork for each user who pushes a deploy. This matches the legacy behavior from CircleCI. (.github/workflows/config.yml) [1] [2]
• A new DEPLOY_NOTIFIER variable is introduced, set to the actual GitHub user who triggered the deploy, for use in notifications. (.github/workflows/config.yml) [1] [2]

Notification messaging:

• The Slack deployment notification now uses DEPLOY_NOTIFIER instead of DEPLOY_USER, so it shows who actually triggered the deployment rather than the Terraform stack identity. (.github/scripts/slackpost_deploy.sh)

Methods

Types of changes

What types of changes does your code introduce?

• Bugfix (non-breaking change which fixes an issue)

Functional tests

N/A

Checklist

• Lint and unit tests pass locally with my changes

Screenshots

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