Petascope_WCPS supports encode format case insensitive

[Bang Pham Huu]

WCPS only supports encode format case sensitive (e.g: "png" or "image/png"). It should support case insensitive also (e.g: "PNG" or "image/pNG").

for c in (Lofoten) return encode(c, "PNG")

 Cannot execute the requested WCPS query, error '<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ows:ExceptionReport version="2.0.1"
    xsi:schemaLocation="http://www.opengis.net/ows/2.0 http://schemas.opengis.net/ows/2.0/owsExceptionReport.xsd"
    xmlns:ows="http://www.opengis.net/ows/2.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink">
    <ows:Exception exceptionCode="WcsError">
        <ows:ExceptionText>Could not serialize coverage metadata, reason 'Encoding format 'PNG' is not supported.'.</ows:ExceptionText>
    </ows:Exception>
</ows:ExceptionReport>