Add data source to retrieve environment variables

[LaurentLesle]

PR Checklist

---

• [ ] I have read the CONTRIBUTING.MD instructions
• [ ] I have changed the resourceDefinition.json
• [ ] I have generated the resource model (there's a models_generated.go file in my PR)
• [ ] I have updated the README.md#resource-status
• [ ] I have checked to ensure there aren't other open Pull Requests for the same update/change?

Description

Add support to retrieve an environment variable

data "azurecaf_environment_variable" "PAT" {
    name           = "PAT_TOKEN"
    fails_if_empty = true
    sensitive      = true
}

Does this introduce a breaking change

• [ ] YES
• [x] NO

Testing

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[BzSpi]

Do you have any example of use case for this feature ? I'm curious :)