FIX: use paging during options generation in edit mode

Summary

Implementation for https://gitlab.com/linkahead/linkahead-webui/-/issues/216

Focus

• Queries that retrieve entities that are candiates for drop down use paging.
• A Count Query identifies whether more enties would be available. If so, an option to enter an ID manually is included (a button ) and the dropdown shows a warning that it does not include all entities.

Test Environment

• manually test the behavior

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src/doc/extension/edit_mode.md

+
+Customizing the Edit Mode
+=========================
+
+
+Customizing the number of candidates retrieved for references in the Edit Mode
+------------------------------------------------------------------------------
+
+To prevent the retrieval of huge numbers of entities just to create candidates
+for the drop down of a reference during editing of an Entity, the number of
+candidates can be limited.
+
+Set the ``BUILD_MAX_EDIT_MODE_DROPDOWN_OPTIONS`` build variable. -1 means no
+limit; every other number is the limit for each query sent (The number of
+candidates can be at most twice this number).