Deprecate FieldMetadataInterface (#13264)

# Introduction

From the moment replaced the FieldMetadataInterface definition to:
```ts
import { FieldMetadataType } from 'twenty-shared/types';

import { FieldMetadataEntity } from 'src/engine/metadata-modules/field-metadata/field-metadata.entity';

export type FieldMetadataInterface<
  T extends FieldMetadataType = FieldMetadataType,
> = FieldMetadataEntity<T>;
```
After this PR merge will create a new one removing the type and
replacing it to `FieldMetadataEntity`.
Did not renamed it here to avoid conflicts on naming + type issues fixs
within the same PR

## Field metadata entity RELATION or MORPH
Relations fields cannot be null for those field metadata entity instance
anymore, but are never for the others see
`packages/twenty-server/src/engine/metadata-modules/field-metadata/types/field-metadata-entity-test.type.ts`
( introduced TypeScript tests )

## Concerns
- TS_VECTOR is the most at risk with the `generatedType` and
`asExpression` removal from interface

## What's next
- `FielMetadataInterface` removal and rename ( see introduction )
- Depcrecating `ObjectMetadataInterface`
- Refactor `FieldMetadataEntity` optional fiels to be nullable only
- TO DIG `never` occurences on settings, defaultValue etc
- Some interfaces will be replaced by the `FlatFieldMetadata` when
deprecating the current sync and comparators tools

packages/twenty-server/src/engine/api/graphql/workspace-schema-builder/utils/generate-fields.utils.ts

@@ -108,7 +108,7 @@ const getTypeFactoryOptions = <T extends FieldMetadataType>(
 ) => {
   return isInputTypeDefinitionKind(kind)
     ? {
-        nullable: fieldMetadata.isNullable,
+        nullable: fieldMetadata.isNullable ?? undefined,
         defaultValue: fieldMetadata.defaultValue,
         isArray:
           kind !== InputTypeDefinitionKind.Filter &&
@@ -117,7 +117,7 @@ const getTypeFactoryOptions = <T extends FieldMetadataType>(
         isIdField: fieldMetadata.name === 'id',
       }
     : {
-        nullable: fieldMetadata.isNullable,
+        nullable: fieldMetadata.isNullable ?? undefined,
         isArray: fieldMetadata.type === FieldMetadataType.MULTI_SELECT,
         settings: fieldMetadata.settings,
         // Scalar type is already defined in the entity itself.