fix(terraform): CKV_AZURE_215 - fix false positive on azurerm_api_management_backend for unresolvable url references

[JoshMcLeanTx]

Description

Fixes #7412

CKV_AZURE_215 produces false positives on azurerm_api_management_backend
when the url parameter is set to a variable reference (var., local., each.,
module., data.) that cannot be statically resolved at scan time. Previously
the check returned FAILED for any URL not containing 'https', including
unresolvable variable references.

New/Edited policies

Description

When a backend url is defined as a variable reference, Checkov cannot
determine the actual value at scan time. Returning FAILED in this case
is a false positive since the URL may well be HTTPS at runtime.

Fix

Configure the url to a hardcoded https:// value, or ensure the variable
resolves to an https:// URL via a variables.tf default value.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my feature, policy, or fix is effective and works
• New and existing tests pass locally with my changes

[JoshMcLeanTx]

Anything needed from my side to get this reviewed? Happy to make any changes.