docs: document table field types customization

Support added in https://github.com/hasura/graphql-engine/pull/5719

Add customization options in the [Table basics -> tracking table](https://hasura.io/docs/latest/graphql/core/databases/postgres/schema/tables.html#tracking-tables) subsection

Also mention possbility and extent of type customizations in the [Table basics -> generated types](https://hasura.io/docs/latest/graphql/core/databases/postgres/schema/tables.html#generated-graphql-schema-types) subsection

Start with PR #5719 and the Table basics → tracking tables subsection in the linked documentation page. Update that subsection with the field-type customization options, then document the possibility and extent of type customizations in the generated GraphQL schema types subsection. Done means both linked sections describe the supported customization behavior.

Written by the indexing model from the issue text.