feat: Add warning when insecure algorithm is used.

[gkwang]

Description

The warning is piped to stderr using console.warn().
Added option to turn it off; defaults to true.

#66

Testing

• 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
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master

[markstos]

For those looking to upgrade to this with only warnings enable, the option that needs to be set is:

 disallowDecryptionWithInsecureAlgorithm: false,

That will continue to allow the insecure algorithms. The warnings are enabled by default and require no flag.