gdal type Byte should sometimes translate to rasdaman type octet

[Bang Pham Huu]

GDAL has a way of distinguishing between signed and unsigned chars:
both have the same data type (Byte), which by default represents an
unsigned char. However, in case the metadata option PIXELTYPE is set to
SIGNEDBYTE, the type Byte means signed char:

PIXELTYPE=[DEFAULT/SIGNEDBYTE]: By setting this to SIGNEDBYTE, a new Byte
file can be forced to be written as signed byte. (from
​https://gdal.org/drivers/raster/gtiff.html)

In LandSupport we have, among others, this type of files (see attachement,
you can use the data on the LS server at the path indicated in the
screenshot for testing).

The task is to update the type translation (gdal → rasdaman) in
wcst_import and petascope to take into account this new aspect (the fact
that some times we must translate Byte to octet), instead of always
translating it to char.