* System user attachment size WIP
* spec check
* controller update
* add max to system_user_max_attachment_size_kb
* DEV: update to use static method for `max_attachment_size_for_user`
add test to use large image.
add check for failure.
* DEV: update `system_user_max_attachment_size_kb` default value to 0
remove unecessary test.
update tests to reflect the new default value of `system_user_max_attachment_size_kb`
* DEV: update maximum_file_size to check when is an attachment made by a system user
Add tests for when `system_user_max_attachment_size_kb` is over and under the limit
Add test for checking interaction with `max_attachment_size_kb`
* DEV: move `max_attachment_size_for_user` to private methods
* DEV: turn `max_attachment_size_for_user` into a static method
* DEV: typo in test case
* DEV: move max_attachment_size_for_user to private class method
* Revert "DEV: move max_attachment_size_for_user to private class method"
This reverts commit 5d5ae0b715.
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Co-authored-by: Gabriel Grubba <gabriel@discourse.org>