Rename FetchMetadata and SetMetadata (with 4 args) to {Fetch,Set}GroupMetadata to resolve override warning. (#5414)

In file included from sdk/core/cpcidskfile.cpp:45:
sdk/segment/metadatasegment.h:59:22: error: 'PCIDSK::MetadataSegment::SetMetadataValue' hides overloaded virtual function
      [-Werror,-Woverloaded-virtual]
        void         SetMetadataValue( const char *group, int id,
                     ^
sdk/segment/cpcidsksegment.h:78:21: note: hidden overloaded virtual function 'PCIDSK::CPCIDSKSegment::SetMetadataValue' declared here: different
      number of parameters (2 vs 4)
        void        SetMetadataValue( const std::string &key, const std::string &value );
                    ^



git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@28171 f0d54148-0727-0410-94bb-9a71ac55c965