Sunset package

[retlehs]

Prepare for package deprecation as of WordPress 6.8, which will include native bcrypt password hashing.

https://make.wordpress.org/core/2025/02/17/wordpress-6-8-will-use-bcrypt-for-password-hashing/

This PR adds:

• Warning notice in README about upcoming redundancy
• Composer conflicts with WordPress >= 6.8

Follow-ups

• Remove this package from https://github.com/roots/bedrock with the release of WordPress 6.8
• Announcement on site: https://roots.io/sunsetting-wp-password-bcrypt-with-wordpress-6-8/
• Update the posts on our site about the package:
  • https://roots.io/improving-wordpress-password-security/
  • https://roots.io/wordpress-password-security-follow-up/
• Remove mentions of wp-password-bcrypt from Bedrock site, docs, README
• Archive this repo
• Mark the package as abandoned on Packagist

Ref #44

[tangrufus]

Add "abandoned": true ?