Update the 'withType' options in 'relationship' fields to allow an array of types

## Description

Currently, in 'relationship' fields in ApostropheCMS 3, the `withType` options only accepts a single string to specify the relationship type. However, in the previous version, ApostropheCMS 2, this property could accept an array of types, allowing for greater flexibility in managing relationships.

### Example

Currently:

_customField: {
label: 'custom',
type: 'relationship',
withType: 'type1',
builders: {
// Include only the information you need with a projection
project: {
title: 1,
_url: 1
}
}
}

Proposal:

_customField: {
label: 'custom',
type: 'relationship',
**withType: ['type1', 'type2']**,
builders: {
// Include only the information you need with a projection
project: {
title: 1,
_url: 1
}
}
}

### Motivation

This change would allow developers to define more complex relationships between content, simplifying data structure and making ApostropheCMS 3 even more powerful and adaptable to project-specific needs.

Thank you for your attention!

Start by locating ApostropheCMS 3's relationship-field handling and the validation or query path for the withType option. Check how the existing single-string case is tested, then add coverage for an array containing type1 and type2; done means both types are accepted and relationships behave as requested.

Written by the indexing model from the issue text.