fixes issue 4691 (#4693)

* bugfix removeprefix not available in python version < 3.9

there was a problem in my cLion gdb that comes with python version 3.8.
the pretty printer script do not work because the removeprefix function is added in version 3.9.
therefore we need a fix for that.

Signed-off-by: Matthias Popp <mpopp@arri.at>

* fix indentation, use the same indentation size at in class JsonValuePrinter

the indentation size was a mix up, we should use always the same indentation size of 4

Signed-off-by: Matthias Popp <mpopp@arri.at>

* use prefix as variable

easier handling or easier to change

Signed-off-by: Matthias Popp <mpopp@arri.at>

* add variables for easier access

Signed-off-by: Matthias Popp <mpopp@arri.at>

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Signed-off-by: Matthias Popp <mpopp@arri.at>
Co-authored-by: Matthias Popp <mpopp@arri.at>