set/unset cron timer for the github actions.
faasr_set_workflow_timer_gh(
faasr,
cred,
actionname,
cron = NULL,
unset = FALSE
)a list form of the JSON file
a list form of the credentials
a string for the target action name
a string for cron data e.g., */5 * * * *
a logical value; set timer(FALSE) or unset timer(TRUE)