Previously hard coded size of 1MB meant any file larger was excluded
from recipient emails - often confusing for CMS admins configuring an
advanced use case for a userform, expecting to recieve files to begin a
business process external to the website.
The configuration has been made to support PHP 'shorthand byte values'
https://www.php.net/manual/en/faq.using.php#faq.using.shorthandbytes
in the configuration option. This give flexibility around oddly
specific limits, but can also be used to set as 0, disabling attachments
Tests are updated to set up a known state before testing, as to be able
to accurately assert the results. One should test the class they intend,
not an Injector service of some unknown element.
