Full-Text Search implementation: /!\ pgsql schema needs to be updated /!\ /!\ Minimal PostgreSQL required version is now 12 /!\ A new options is available to specify main language of a node. By default a `generic` language is used (which uses the `simple` configuration in PostgreSQL). When a node owner changes the language, the index is rebuilt accordingly. It is possible to have item specific language for multilingual nodes (but for the moment the search is done with node language, so the results won't be good). If an item language is explicitely set in `item_languages`, the FTS configuration won't be affected by node FTS language setting. Search is parsed with `websearch_to_tsquery` for now, but this parser doesn't handle prefix matching, so it may be replaced in the future. SetConfiguration now only updates the modified values, this avoid triggering the FTS re-indexing on each config change. `_checkNodeExists` is not called anymore as we can check if a row has been modified to see if the node exists, this avoid a useless query. Item storing has been slighly improved with a useless SELECT and condition removed. To avoid 2 schema updates in a row, the `sat_pubsub_update_5_6.sql` file also prepares the implementation of XEP-0346 by updating nodes with a schema and creating the suitable template nodes.