Issue #3508976: Allow 'custom' custom fields to be supported

...l_type/src/SchemaDotOrgAdditionalTypeManagerInterface.php

...SchemaDotOrgContentModelDocumentationManagerInterface.php

...chemadotorg_custom_field/schemadotorg_custom_field.module

...otorg_custom_field/src/SchemaDotOrgCustomFieldManager.php

...tom_field/src/SchemaDotOrgCustomFieldManagerInterface.php

...s/src/Kernel/SchemaDotOrgCustomFieldManagerKernelTest.php

.../Config/SchemaDotOrgDescriptionsConfigFactoryOverride.php

...s/schemadotorg_diagram/src/SchemaDotOrgDiagramBuilder.php

.../schemadotorg_epp/src/SchemaDotOrgEppManagerInterface.php

...c/SchemaDotOrgFieldGroupEntityDisplayBuilderInterface.php

...adotorg_jsonld/src/SchemaDotOrgJsonLdBuilderInterface.php

...adotorg_jsonld/src/SchemaDotOrgJsonLdManagerInterface.php

...endpoint/src/Routing/SchemaDotOrgJsonLdEndpointRoutes.php

...preview/src/SchemaDotOrgJsonLdPreviewBuilderInterface.php

...aphs/src/SchemaDotOrgLayoutParagraphsManagerInterface.php

...es/schemadotorg_ui/src/Form/SchemaDotOrgUiMappingForm.php

src/Element/SchemaDotOrgAutocomplete.php

src/SchemaDotOrgEntityDisplayBuilderInterface.php

src/SchemaDotOrgEntityFieldManagerInterface.php

src/SchemaDotOrgInstaller.php