style: Modify access modifiers for config and request

[ci0n]

I encountered the same issue as #55, and I hope to extend the functionality of the SDK through the internal request method.

example:

import { SDK } from 'casdoor-nodejs-sdk';

export class Casdoor extends SDK {

  public async getAuthTokenByPassword(username: string, password: string) {
    if (!request) {
      throw new Error('request init failed')
    }

    const {
      data: { access_token, refresh_token },
    } = (await this.request.post('login/oauth/access_token', {
      client_id: this.config.clientId,
      client_secret: this.config.clientSecret,
      grant_type: 'password',
      username,
      password,
    })) as unknown as AxiosResponse<{
      access_token: string
      refresh_token: string
    }>

    return {
      access_token,
      refresh_token,
    }

  }

}

[casbin-bot]

@tangyang9464 @imp2002 please review

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[hsluoyz]

Replaced by: 06989b1