Consider WordPress performance options

[jpmckinney]

If we notice performance issues. Right now, on the public sites, I'm getting high 90s on Google Chrome's Lighthouse tab, and A grades on GTmetrix, for both www.open-spending.eu and the draft www.open-contracting.org.

• OPcache https://www.php.net/manual/en/book.opcache.php
  • Ben Everard (at Idea Bureau) would need access to a command to restart OPCache (usually via php-fpm), during deployments
• Redis Object Cache https://wordpress.org/plugins/redis-cache/
  • We might need to review existing cache plugins/configuration with Ben Everard. www.open-contracting.org is using https://wordpress.org/plugins/w3-total-cache/ (w3tc)
• We intend to upgrade to PHP 8.3 when upgrading to Ubuntu 24 (i.e. when changing servers).
  • Ben Everard might need to make minor adjustments to composer.json, similar to https://github.com/open-contracting-partnership/website/pull/33/files