Give the possibiltiy to add custom variables to the matomo configuration variable

[Chardonneaur]

Hi Ronan,

Currently within the Matomo configuration variable it is possible to define custom dimensions but not custom variables.
Custom variables are the only way to support lists as values: https://matomo.org/faq/general/faq_21117/.
Would it be possible for you to add this option?
Thank you,