Add ability to verify claim presence

[jimmyjames]

Changes

As raised in #360, we should provide the ability to verify a claim's presence, regardless of value.

This change adds a new Verification method, withClaimPresence(String name). It will throw an InvalidClaimException if the JWT does not contain the specified claim.

This change does not add the ability to verify a claim is present and of a specific type. That may be a feature we wish to add at some point, but we'd need to consider how best to surface that without exposing any of Jackson's node types. Such a change wouldn't impact the new method added in this PR, so we can still provide value here with the new presence check method.

References

#360

Testing

• This change adds test coverage
• This change has been tested on the latest version of Java or why not

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors