Make Sending Lab column in RKI report csv adjustable via the config file

[thomasbtf]

Make Sending Lab column in RKI csv adjustable via the config file. Add ad new parameter to the rule rki_report (https://github.com/IKIM-Essen/uncovar/blob/master/workflow/rules/generate_output.smk#L83), which replaces the hardcoded Sending Lab number from UK-Essen.
https://github.com/IKIM-Essen/uncovar/blob/master/workflow/scripts/generate-rki-output.py#L25

Moreover, we can use the date of the current run (wildcards.date) to refill the column DATE_DRAW (https://github.com/IKIM-Essen/uncovar/blob/master/workflow/scripts/generate-rki-output.py#L26).