@property.array doesn't work if nulls are allowed

Nobody has claimed this yet.

### Describe the bug

Trying to make a model that maps to a nullable JSON or array column in PostgreSQL, so the entity property needs to permit nulls.

A property declared like this:
```typescript
@property.array('string', {
required: false,
})
foo!: string[] | null;
```
Produces a `@property.array can only decorate array properties` from here: https://github.com/loopbackio/loopback-next/blob/a60ae8e43a1ec9d65929f19bbd364e332f28503b/packages/repository/src/decorators/model.decorator.ts#L155

Trying to "hack" it like this:
```typescript
@property({
required: false,
type: Array,
itemType: 'string',
jsonSchema: {
type: 'array',
nullable: true,
items: { type: 'string' },
},
})
```
Results in incorrect data being sent to PostgreSQL (get JSON syntax errors because it's sending the object as an array to the PG driver instead of the `JSON.stringify` it should be using, because the array check in `loopback-connector-postgresql` (https://github.com/loopbackio/loopback-connector-postgresql/blob/61b5029275487fc7812d774ab4be16dc8aacd726/lib/postgresql.js#L788) fails

### Logs

_No response_

### Additional information

_No response_

### Reproduction

https://codesandbox.io/s/zen-thompson-keo2is

Read packages/repository/src/decorators/model.decorator.ts at the reported array-property check, then compare it with the array handling in loopback-connector-postgresql/lib/postgresql.js. Reproduce the nullable array case with the linked CodeSandbox and verify that the decorator accepts it and PostgreSQL receives valid JSON without syntax errors.

Written by the indexing model from the issue text.