wordpress-fargate: modernize encryption settings

[jre21]

This pull request consists of two changes: encrypting EFS's file storage, and restricting the TLS settings to only use modern ciphers. Web browsers have already started disabling earlier TLS versions; at this point allowing older ciphers just increases attack surface without meaningfully improving compatibility with existing web clients, and I'd rather see settings that are secure by default.

I'm open to adding variables to configure TLS settings rather than hardcoding them in cloudfront.tf and alb.tf, if that would be a preferred approach.