feat: update to azurermv4

[jtracey93]

Move to azurerm v4.0 minimum version

Fixes #60

Type of Change

• Non-module change (e.g. CI/CD, documentation, etc.)
• Azure Verified Module updates:
  • Bugfix containing backwards compatible bug fixes
    • Someone has opened a bug report issue, and I have included "Closes #{bug_report_issue_number}" in the PR description.
    • The bug was found by the module author, and no one has opened an issue to report it yet.
  • Feature update backwards compatible feature updates.
  • Breaking changes.
  • Update to documentation

Checklist

• I'm sure there are no other open Pull Requests for the same update/change
• My corresponding pipelines / checks run clean and green without any errors or warnings
• I did run all pre-commit checks

Copilot reviewed 4 out of 9 changed files in this pull request and generated no comments.

Files not reviewed (5)

• examples/custom-zones-vnet-link-existing-rg/main.tf: Language not supported
• examples/default/main.tf: Language not supported
• examples/with-vnet-link-existing-rg/main.tf: Language not supported
• main.tf: Language not supported
• terraform.tf: Language not supported