Allow targeting WP install version via args, tags, utility script

[leonstafford]

feedback from user:

1. Configure the WP version to install — ironic, I know. While migrating a 10+ year old blog, I discovered its theme only worked correctly with wordpress 5.4.4. Don't know if that's a normal wordpress problem, but downgrading via WP CLI worked without issue, so the workaround only took a minute to get up and running again.

[leonstafford]

to keep maintenance a bit simpler, prefer to offer just 2 main image types: php7.4 and php8.0 (similar naming to WP's Docker images), along with versioned tags to control what's served via the website's 1-liner, ie php7.4-0.0.1, php7.4-0.0.2.

Website uses a version number to bust cache, but can also map to a version within the lokl-go launcher script.

I'll keep the 1-liner mapping to the php 7.4 images, but offer php 8 images via a different command/version.

PHP 8 version currently running nightly WP, but should switch to 5.6 RC# as expected PHP 8 compatible version.

Unexpected that many users would want nightly and for those, can switch on instantiated image via WP_CLI or a Lokl command as per this issue