Update voter documentation for supportsAttribute and supportsClass deprecation

[weaverryan]

See symfony/symfony#15151

This may only be components/security/authorization.rst

[Koc]

cookbook/security/voters.rst also requires changes

[weaverryan]

Further updated at symfony/symfony#16601

[weaverryan]

PR added

[weaverryan]

Ah, the best_practices/security.rst also needs to be updated.