Use a parameter to define the maximum number of messages to process at once for the SOSMailReadInbox job

Description
The SOSMailReadInbox job (class sos.mail.SOSMailProcessInbox) gets elements from a e-mail inbox. The number of elemts to be processed in parallel is limited to 1000.
Desired behaviour
The value for the maximum number of messages that are to be processed at once should be a configurable parameter for the job.
Solution
Please use the new parameter max_mails_to_process, default=1000 to specify the maximum number of emails that should be processed.