Replace backoff in elastic requests

[a-ovchinnikov]

Currently backoff is used for retrying failed requests to external services. The project appears abandoned. It also does not play well with UTs when more requests are made elastic. At the same time the necessary functionality could be trivially added as an utility decorator and maintained in project's code base.

Acceptance criteria:

1. retry decorator is added with the following capabilities:
   a. linear and exponential retries;
   b. adjustable number of retries;
   c. adjustable delay;
   d. adjustable retry conditions (i.e. ability to select on which exceptions to retry).