Add skipXmlComments as internal arg for OWS http XML requests

[Emmanuel Blondel]

By default, an skipXmlComments will be set to TRUE for any OWS HTTP request. This will be applied to remove eventual comments on the service XML response, now done systematically by default on XML requests.

In the case of WFS, for large data requests, this can be a bottleneck resulting in vector memory allocation errors, as spotted out in EMODnet/EMODnetWFS#164 This small enhancement will set skipXmlComments to FALSE for the WFS GetFeatures, likely not to contain XML comments, as we could find in ISO metadata for example.