Modify rule S5856: Add language Rust (#4678)

* Add rust to rule S5856

* Add rule description

* Fix header

* Add Clippy tag and link to Clippy lint

---------

Co-authored-by: sallaigy <sallaigy@users.noreply.github.com>
Co-authored-by: Gyula Sallai <gyula.sallai@sonarsource.com>
Co-authored-by: yassin-kammoun-sonarsource <yassin.kammoun@sonarsource.com>

rules/S5856/rust/metadata.json

@@ -0,0 +1,6 @@
+{
+  "tags": [
+    "regex",
+    "clippy"
+  ]
+}

rules/S5856/rust/rule.adoc

@@ -0,0 +1,41 @@
+== Why is this an issue?
+
+include::../description.adoc[]
+
+=== Noncompliant code example
+
+[source,rust,diff-id=1,diff-type=noncompliant]
+----
+Regex::new("(")
+----
+
+
+=== Compliant solution
+
+[source,rust,diff-id=1,diff-type=compliant]
+----
+Regex::new("\(")
+----
+
+== Resources
+
+=== Documentation
+
+* Regex crate documentation - https://crates.io/crates/regex[regex]
+* Clippy Lints - https://rust-lang.github.io/rust-clippy/master/index.html#invalid_regex
+
+ifdef::env-github,rspecator-view[]
+
+'''
+== Implementation Specification
+(visible only on this page)
+
+=== Message
+
+Invalid regular expression syntax.
+
+=== Highlighting
+
+The error inside the regular expression
+
+endif::env-github,rspecator-view[]