Introduce new /$DB/-/query endpoint, soft replaces /$DB?sql=... (#2363)

* Introduce new default /$DB/-/query endpoint
* Fix a lot of tests
* Update pyodide test to use query endpoint
* Link to /fixtures/-/query in a few places
* Documentation for QueryView

---------

Co-authored-by: Simon Willison <swillison@gmail.com>

docs/pages.rst

@@ -55,6 +55,21 @@ The following tables are hidden by default:
 - Tables relating to the inner workings of the SpatiaLite SQLite extension.
 - ``sqlite_stat`` tables used to store statistics used by the query optimizer.
 
+.. _QueryView:
+
+Queries
+=======
+
+The ``/database-name/-/query`` page can be used to execute an arbitrary SQL query against that database, if the :ref:`permissions_execute_sql` permission is enabled. This query is passed as the ``?sql=`` query string parameter.
+
+This means you can link directly to a query by constructing the following URL:
+
+``/database-name/-/query?sql=SELECT+*+FROM+table_name``
+
+Each configured :ref:`canned query <canned_queries>` has its own page, at ``/database-name/query-name``. Viewing this page will execute the query and display the results.
+
+In both cases adding a ``.json`` extension to the URL will return the results as JSON.
+
 .. _TableView:
 
 Table