[services] Blob - Get Reactor - Fix initialize logic

Summary: I spotted that the logic in GetReactor::initialize is a bit odd and contains duplicated logic. I think it can be simplified as it is done in this diff.

Test Plan:

• terminal 1

cd services
yarn run-blob-service-in-sandbox

• terminal 2

cd services
yarn run-integration-tests blob

Reviewers: tomek, max

Reviewed By: tomek

Subscribers: ashoat, tomek, adrian, atul, abosh

Differential Revision: https://phab.comm.dev/D4649