Add constructor with custom HttpClient supplier

[TheFaser]

This PR adds a new constructor that allows overriding OkHttpClient while keeping the default ObjectMapper

Problem

Current constructors require both ObjectMapper and HttpClient suppliers. This causes issues when ObjectMapper is relocated to a different namespace

Solution

public TelegramBotsLongPollingApplication(Supplier<OkHttpClient> okHttpClientCreator) {
    this(ObjectMapper::new, okHttpClientCreator);
}