adds interpolation grid interface yac_interp_grid_get_src_grid_name and yac_interp_grid_get_tgt_grid_name

This reverts commit 58da9830.

* most fields are synchronised by routine yac_couple_config_field_merge and are not required to be sent in the initial exchange

renames routine yac_couple_config_get_collection_size to yac_couple_config_get_field_collection_size

adds argument max_search_distance to routine yac_interp_grid_do_nnn_search_src and yac_interp_grid_do_nnn_search_tgt