feat: Support Bearer authorization callback in operations

[ffflorian]

This supports adding a callback to an endpoint which uses Bearer authorization:

deleteExchange = async (
  id: number,
  accessTokenCallback: () => Promise<string>
): Promise<void> => {
  const accessToken = await accessTokenCallback();
  const config: AxiosRequestConfig = {
    headers: {
      Authorization: `Bearer ${decodeURIComponent(accessToken)}`,
    },
    method: 'delete',
    url: `/api/v1/exchange/${id}`,
  };
  await this.apiClient.request(config);
};

I also moved from this.apiClient.[method]() to this.apiClient.request() and moved the method to the axios request configuration.

This closes #62.