Fix cryptographically insecure ID generation

[tomauth0]

Description

The existing methods of ID generation are not cryptographically secure. This PR introduces the id-generation lib - a lightweight lib for generating suitably random IDs with a given dictionary. Utils.js updated to make use of this lib

Also used the opportunity to cleanup some of the utils file - swapping out vars and removing some unneeded syntax

References

https://github.com/auth0/node-samlp/issues/111

Testing

Unit tests added for ID length and dictionary memebership

• [x] This change adds test coverage for new/changed/fixed functionality

Checklist

• [ ] I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• [x] All active GitHub checks for tests, formatting, and security are passing
• [x] The correct base branch is being used, if not master