Introduced the ability to listen for the correct completion of each request.

[LosDanieloss]

I've encountered similar issue to the one described in issue #109 . Thought that will be cool to be able to observe successful response per request not as whole initialization. It's because as explained in mentioned issue init will fail if even single request fail but actually now() will return time even if only one request succeeded. So here is my proposed solution. It'll allow to know if at least one request during synchronization succeeded or will allow the user of the library want he/she could implement some sort of threshold of successful requests like author of issue #109 suggested.

[kaushikgopal]

@LosDanieloss 🙏 thank you so much for these changes. TrueTime has since undergone massive changes with the migration to Kotlin + Coroutines.

I did take your suggestion however and added a parameter now called strictNtpMode which effectively does what you're suggesting. Feel free to reopen if you have more suggestions/comments.