Add retry support for manual python writer

[yirutang]

Pretty much all customers will have to deal with connection level retry when using bi-di streaming API.

For customers who is not aware of this, they went into issues and open support ticket on us. To reduce support toil, we really need to have connection level retry done for them (ideally we have some support in the in-stream error retry as well).

We could do similar things as we did in nodejs library:
https://github.com/googleapis/nodejs-bigquery-storage/pull/443/files

I will be happy to review the code and assist with the testing.