Fix G_TYPE_STRING json formatting
Fix G_TYPE_STRING json formatting

Using g_strdup_value_contents to get a string will result in debug
style formatting not suitable for use with json due to extra quotes.

RidgeRun/gstd-1.x,RidgeRun/gstd-1.x,RidgeRun/gstd-1.x,RidgeRun/gstd-1.x