Strapi 5 | getFetchClient only works for JSON
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## Bug report

### Required System information

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- Node.js version: 20
- NPM version: 8
- Strapi version: 5.6.0
- Database: PostgreSQL
- Operating system: Win 11 Pro
- Is your project Javascript or Typescript: Javascript

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### Describe the bug

The `getFetchClient` provides utility functions to communicate with the admin routes. In v4, axios was used. In v5 the JS fetch API is used. When doing get calls, this net getFetchClient defaults to using .json(). See https://github.com/strapi/strapi/blob/146a31b564bc8232686331f6b28f7ff966817963/packages/core/admin/admin/src/utils/getFetchClient.ts#L123
This makes it impossible to use it with other data types like text. The most common example might be the usage with CSV data. Since it defaults to json, the data would always be empty when the controller returns `text/csv`.

### Steps to reproduce the behavior

1. Create a router/controller that returns text/csv.
2. Use the get function of the getFetchClient
3. Data is empty, because it defaults to JSON

### Expected behavior

getFetchClient should support other data types than JSON. In v4 this worked without issue due to using axios.

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### Additional context

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