Typescript: Object literal may only specify known properties, and 'min' does not exist in type

**Describe the bug**

If we define a `relation` field with `multiple: true` and `min` or `max` we get the following typescript typings error

```
Object literal may only specify known properties, and 'min' does not exist in type '(CmsFieldBase & CmsFieldRelation) | (CmsFieldBase & CmsFieldMeta)'.
```

**To Reproduce**

1. Have a project using Typescript
2. Have your CMS schema defined in typescript

Sample code:

```ts
import CMS from 'netlify-cms-app';

const local_backend = process.env.NODE_ENV === 'development';

CMS.init({
config: {
local_backend,
load_config_file: false,
backend: {
name: 'git-gateway',
branch: 'main',
},
collections: [
{
name: 'pages',
label: 'Pages',
folder: 'cms/content/pages',
create: false,
slug: '{{slug}}',
fields: [
{
label: 'Fund Types',
name: 'fundTypes',
widget: 'relation',
collection: 'Options',
search_fields: ['label'],
value_field: 'label',
multiple: true,
min: 1, // we get the error here
},
],
},
],
},
});
```

**Expected behavior**

No typescript error should occur, because `min` and `max` are valid relation properties

**Screenshots**

**Applicable Versions:**

- "netlify-cms-app": "^2.15.72",

**CMS configuration**

```ts
import CMS from 'netlify-cms-app';

const local_backend = process.env.NODE_ENV === 'development';

CMS.init({
config: {
local_backend,
load_config_file: false,
backend: {
name: 'git-gateway',
branch: 'main',
},
collections: [
{
name: 'pages',
label: 'Pages',
folder: 'cms/content/pages',
create: false,
slug: '{{slug}}',
fields: [
{
label: 'Fund Types',
name: 'fundTypes',
widget: 'relation',
collection: 'Options',
search_fields: ['label'],
value_field: 'label',
multiple: true,
min: 1, // we get the error here
},
],
},
],
},
});
```

**Additional context**