Create rule S6437: Credentials should not be hard-coded (#4641)

* Add go to rule S6437

* Add description for S6437 for Go

---------

Co-authored-by: daniel-teuchert-sonarsource <daniel-teuchert-sonarsource@users.noreply.github.com>
Co-authored-by: Daniel Teuchert <daniel.teuchert@sonarsource.com>

rules/S6437/go/metadata.json

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+{
+}

rules/S6437/go/rule.adoc

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+include::../../../shared_content/secrets/description.adoc[]
+
+== Why is this an issue?
+
+include::../../../shared_content/secrets/rationale.adoc[]
+
+=== What is the potential impact?
+
+include::../common/impact/rationale.adoc[]
+
+include::../../../shared_content/secrets/impact/financial_loss.adoc[]
+
+include::../../../shared_content/secrets/impact/security_downgrade.adoc[]
+
+== How to fix it
+
+include::../../../shared_content/secrets/fix/revoke.adoc[]
+
+include::../../../shared_content/secrets/fix/recent_use.adoc[]
+
+include::../../../shared_content/secrets/fix/vault.adoc[]
+
+=== Code examples
+
+include::../common/fix/code-rationale.adoc[]
+
+==== Noncompliant code example
+
+[source,go,diff-id=1,diff-type=noncompliant]
+----
+import (
+    "net/url"
+)
+
+func main() {
+    url.UserPassword("user", "password") // Noncompliant
+}
+----
+
+==== Compliant solution
+
+[source,go,diff-id=1,diff-type=compliant]
+----
+import (
+    "net/url"
+    "os"
+)
+
+func main() {
+    url.UserPassword(os.Getenv("USER"), os.Getenv("PASSWORD"))
+}
+----
+
+include::../common/fix/how-it-works.adoc[]
+
+== Resources
+
+include::../common/resources/documentation.adoc[]
+
+include::../common/resources/standards.adoc[]
+
+ifdef::env-github,rspecator-view[]
+'''
+== Implementation Specification
+(visible only on this page)
+
+=== Message
+
+Revoke and change this password, as it is compromised.
+
+=== Highlighting
+
+Highlight the credential use and its initialization.
+
+'''
+endif::env-github,rspecator-view[]