Update action and script to allow for theme choice

[joemcgill]

This PR makes a few updates to the GitHub action and related CLI script to allow someone running either workflow determine the individual theme that is being tested, rather than hard coding both the twentytwentyone and twentytwentythree themes and running them in sequence, which we've found causes the benchmarks for the second theme to be effected by changes to the environment during tests of the first theme.

GitHub action workflow
The GH action has been updated so that the twentytwentyfour theme is installed on the environments and the workflow can be run by choosing either twentytwentyone, twentytwentythree, or twentytwentyfour from the UI:

CLI script
The CLI script has been modified so the third parameter is now the theme slug that you want to test. Example:

./run.sh https://wordpress.org/wordpress-6.3.2.zip https://wordpress.org/wordpress-6.4-RC2.zip twentytwentythree

Additionally, the environment vars are updated to turn off Cron (DISABLE_WP_CRON: true) while running benchmarks to keep scheduled tasks from effecting the results during benchmarking runs.

[swissspidy]

Additionally, the environment vars are updated to turn off Cron (DISABLE_WP_CRON: true) while running benchmarks to keep scheduled tasks from effecting the results during benchmarking runs.

There's a lot more to be done in this regard (cleanup / reset / reducing variance), e.g. disabling external HTTP calls. But it's a start 👍