Relation widget slow on initial load

**Describe the bug**
We're using the relations widget to select authors for articles. This was fine to begin with. However, as the number of authors increased the load time increased drastically.

From other issues I understand that each a request is sent for each file and those should be cached after the initial load. However, our authors typically open this widget once.

Number of authors in collection: ~200

**To Reproduce**
Assuming the collections exist and one of the collections have relation to another collection

1. Create a new item (or select an existing one)
2. Click the dropdown

**Expected behavior**
Faster load time. A couple of seconds for example.

A possible solution could be that the search functionally limited the number of requests.

**Applicable Versions:**
- Netlify CMS version: 2.13.3
- Browser version: Latest chrome and firefox

**CMS configuration**

```yaml
collections:
- name: post_javascript
label: 'Post: JavaScript'
folder: post/javascript
create: true
summary: '{{post_year}}/{{post_day}}: {{title}}'
fields:
- { label: 'Calendar', name: 'calendar', widget: 'hidden', default: 'javascript' }
- {
label: 'Year',
name: 'post_year',
widget: 'number',
default: 2020,
valueType: 'int',
min: 2018,
max: 2021,
}
- {
label: 'Day',
name: 'post_day',
widget: 'number',
default: 1,
valueType: 'int',
min: 1,
max: 24,
}
- { name: title, label: Title }
- { name: image, label: 'Link to image', required: false }
- { name: ingress, label: 'Ingress', widget: markdown, required: false }
- { name: description, label: 'SEO Description', widget: text, required: false }
- { name: body, label: Body, widget: markdown }
- name: links
label: 'Relevant links'
widget: list
fields:
- { name: title, label: Title }
- { name: url, label: Url }
- name: authors
label: 'Authors'
widget: list
field:
{
label: 'Author',
name: 'author',
widget: 'relation',
collection: 'authors',
searchFields: ['title'],
valueField: 'title',
displayFields: ['title'],
- name: authors
label: Authors
folder: authors
create: true
fields:
- { name: title, label: Name }
- {
name: socialMediaLink,
label: 'Link to social media (twitter, linkedin etc.)',
required: false,
}
- { name: 'company', label: 'Company', default: 'Bekk' }
```