NEW - New setting in wcst_import to set wms style + legend

[Bang Pham Huu]

The new setting wms_styles as an array allow to add styles to a layer shortly after the time of creating new coverage via WCS-T InsertCoverage request when wms_import is set to: true.

"wms_styles":
[
 {
  "name": "Style 1",
  "title": "Style title",         // required
  "abstract": "Style description",// required
  "default": true,                // optional, false by default
  "wcps_query_fragment": "..",    // optional; exclusive with rasql_query_fragment
  "rasql_query_fragment": "..",   // optional; exclusive with wcps_query_fragment

  "gdal_color_table": "gdal.json",// optional; exclusive with sld_color_table, color_map
  "sld_color_table": "sld.xml",   // optional; exclusive with gdal_color_table, color_map
  "color_map": "ColorMap.json"    // optional; exclusive with gdal_color_table, sld_color_table

  "legend": "legend.png"          // optional
 },
 { ... }
]