[MENFORCER-517] requireReleaseDeps ignores optioanal dependencies

**[James Nord](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=jnord_cbs)** opened **[MENFORCER-517](https://issues.apache.org/jira/browse/MENFORCER-517?redirect=false)** and commented

A project configured with an optional dependency with a snapshot version and enforcer with `requireReleaseDeps` set to fail should fail the build, however the rule does not look at optional dependencies.

Whilst this makes not difference to consumers, it means that  `requireReleaseDeps` can not be used to help enforce the reproducibility of release builds.

### Steps to Reproduce

create a maven pom with the following: 

```java

  4.0.0  maven.test
  enforcer-bug
  jar
  1-SNAPSHOT 
   
     
       
          maven-enforcer-plugin
          3.5.0
       
     
       
     
        maven-enforcer-plugin
       
         
            enforce-no-snapshots
           
              enforce
           
           
             
               
                  No Snapshots Allowed For Release Versions
                  false
               
             
              true
              false
           
         
       
     
   
   
   
      junit
      junit
      4.1-SNAPSHOT
      jar
      test
      true
   
 

```

run `mvn validate`

### Expected results

The build fails with

```java
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:3.5.0:enforce (enforce-no-snapshots) on project enforcer-bug:
[ERROR] Rule 0: org.apache.maven.enforcer.rules.dependency.RequireReleaseDeps failed with message:
[ERROR] No Snapshots Allowed For Release Versions
[ERROR] maven.test:enforcer-bug:jar:1-SNAPSHOT
[ERROR]    junit:junit:jar:4.1-SNAPSHOT <--- is not a release dependency
```

### Actual results

the build passes

```java
[INFO] Rule 0: org.apache.maven.enforcer.rules.dependency.RequireReleaseDeps passed
```

Note if you remove the `true` from the dependency you will see that the enforcer rule passes

---

**Affects:** 3.5.0

Start with the org.apache.maven.enforcer.rules.dependency.RequireReleaseDeps rule described in the issue and reproduce the case using the supplied Maven POM. Run `mvn validate` with an optional snapshot dependency and compare the result with the expected failure. Done means requireReleaseDeps rejects the optional snapshot dependency as shown.

Written by the indexing model from the issue text.