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#### Is your feature request related to a problem? Please describe.
While trying to migrate to the new FormData autogeneration (by using postForm or setting Content-Type to multipart) I realized arrays won't work anymore. An 'arr' proprety with two entries will be converted to name="arr.0" and name="arr.1" in the payload.
I saw in the source-code that once the name has a suffix like '[]' it will post it as such. But our springboot backend wants the key to be 'arr' (not 'arr[]') and our client-side typescript interface has a key named 'arr' and not 'arr[]' either.

#### Describe the solution you'd like
Plain arrays should also be send automatically, without the need to put '[]' to its name. If that's a breaking change, make it optional via options.

#### Describe alternatives you've considered
Springboot can't parse the default 'arr.0', 'arr.1' format. And adding '[]' to the type, the client-side object and the desired property in the backend is not an ideal solution.

In typescript properties of types/interfaces usually don't have a '[]' suffix. But the whole point of migrating to this new feature is to have type-safe services with a typed payload instead of just any 'FormData' object.

#### Additional context

index.d.ts
onse?: AxiosResponse<T, D>
  );
  config?: AxiosRequestConfig<D>;
  code?: string;
  request?: any;
  response?: AxiosResponse<T, D>;
  isAxiosError: boolean;
  status?: string;
  toJSON: () => object;
  static readonly ERR_FR_TOO_MANY_REDIRECTS = "ERR_FR_TOO_MANY_REDIRECTS";
  static readonly ERR_BAD_OPTION_VALUE = "ERR_BAD_OPTION_VALUE";
  static readonly ERR_BAD_OPTION = "ERR_BAD_OPTION";
  static readonly ERR_NETWORK = "ERR_NETWORK";
  static readonly ERR_DEPRECATED = "ERR_DEPRECATED";
  static readonly ERR_BAD_RESPONSE = "ERR_BAD_RESPONSE";
  static readonly ERR_BAD_REQUEST = "ERR_BAD_REQUEST";
  static readonly ERR_CANCELED = "ERR_CANCELED";
  static readonly ECONNABORTED = "ECONNABORTED";
  static readonly ETIMEDOUT = "ETIMEDOUT";
}
export class CanceledError<T> extends AxiosError<T> {
}
export type AxiosPromise<T = any> = Promise<AxiosResponse<T>>;
export interface CancelStatic {
  new (message?: string): Cancel;
}
export interface Cancel {
  message: string | undefined;
}
export interface Canceler {
  (message?: string): void;
}
export interface CancelTokenStatic {
  new (executor: (cancel: Canceler) => void): CancelToken;
  source(): CancelTokenSource;
}
export interface CancelToken {
  promise: Promise<Cancel>;
  reason?: Cancel;
  throwIfRequested(): void;
}
export interface CancelTokenSource {
  token: CancelToken;
  cancel: Canceler;
}
export interface AxiosInterceptorOptions {
  synchronous?: boolean;
  runWhen?: (config: AxiosRequestConfig) => boolean;
}
export interface AxiosInterceptorManager<V> {
  use<T = V>(onFulfilled?: (value: V) => T | Promise<T>, onRejected?: (error: any) => any, options?: AxiosInterceptorOptions): number;
  eject(id: number): void;
}
export class Axios {
  constructor(config?: AxiosRequestConfig);
  defaults: AxiosDefaults;
  interceptors: {
    request: AxiosInterceptorManager<AxiosRequestConfig>;
    response: AxiosInterceptorManager<AxiosResponse>;
  };
  getUri(config?: AxiosRequestConfig): string;
  request<T = any, R 