Overhaul custom entities page (#676)

* remove references to dataclass objects

* Fix a copy-paste error.

* remove extra file

* Fix a copy-paste error.

* Remove unused file

* Update Quickstart to use explicit schema

* Update custom_dc/quickstart.md

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* Changes from Keyur

* Remove references to implicit schema in the custom data page

* Remove implicit schema from config reference

* More changes

* Update custom_dc/config.md

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* Update custom_dc/custom_data.md

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* add explanation of format option

* Start work on overhaul of custom entities page

* Finish first draft of overhaul of custom entities page

* More changes

* minor tweaks

* Update custom_dc/custom_entities.md

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Update custom_dc/custom_entities.md

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Update custom_dc/custom_entities.md

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Fixes from Gemini

* Add character limit to entity definitions

* Fix CSV formatting

* Incorporate changes from Keyur

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Author: kmoscoe