Consider changing naming of getSurfaceDirectory and getPolygonsDirectory to use ...MetaList

[jorgenherje]

The router endpoints are returning list of respective Meta, i.e. SurfaceMeta and PolygonsMeta.

Change the naming of routers to match actual returned data type, and not use naming Directory.

The front-end code can use the the new useSurfaceDirectoryQuery -> useSurfaceMetaListQuery to create a surfaceDirectory object as already done. The same can be done for the equivalent new usePolygonsDirectoryQuery -> usePolygonsMetaListQuery.

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See the same work done for get_seismic_directory -> get_seismic_cube_meta_list in #449