Modify rule S6945: Add MAINTAINABILITY quality, increase severity and impact levels (#4707)

* Modify rule S6945: Add MAINTAINABILITY quality.

S6945 does not necessarily indicate a bug since COND might not be set on
purpose.
Hence, keeping the type as `CODE_SMELL` appears correct.

However, as a code smell, we need to qualify its `MAINTAINABILITY` impact.

At the same time, we keep the existing `RELIABILITY` impact:
Not setting COND is a practice that not only leads to harder to debug code but
it may also lead to bugs

* Modify rule S6945: Upgrade severity and impact to Critical and HIGH

Following the documentation, MAINTAINABILITY issues should have at least HIGH
impact, and Critical severity, if they can lead to the introduction of bugs.

RELIABILITY issues should have at least HIGH impact, and Critical severity,
if they can for example cause corrupted data.

Both applies here. Hence, we upgrade the `defaultSeverity` and impact
levels.

These are the documentation link:
https://docs.sonarsource.com/sonarqube-server/2025.1/extension-guide/adding-coding-rules/#setting-severities-in-mqr-mode
https://docs.sonarsource.com/sonarqube-server/2025.1/extension-guide/adding-coding-rules/#setting-severities-in-se-mode

rules/S6945/jcl/metadata.json

@@ -8,7 +8,7 @@
   },
   "tags": [
   ],
-  "defaultSeverity": "Major",
+  "defaultSeverity": "Critical",
   "ruleSpecification": "RSPEC-6945",
   "sqKey": "S6945",
   "scope": "All",
@@ -16,7 +16,8 @@
   "quickfix": "unknown",
   "code": {
     "impacts": {
-      "RELIABILITY": "MEDIUM"
+      "RELIABILITY": "HIGH",
+      "MAINTAINABILITY": "HIGH"
     },
     "attribute": "LOGICAL"
   }