integrate new account storage iterator

[BeniaminDrasovean]

Reasoning behind the pull request

• The leavesRetriever (here is the implementation) component was not integrated

Proposed changes

• Integrate the leavesRetriever and refactor it to be stateless
• Add new API endpoint /address/iterate-keys. This will be a POST request. The request has numKeys, address, and iteratorState. If the iterator state is empty, the iteration will begin from the rootHash. If numKeys is 0, the iteration will stop either when all the leaves have been retrieved or when the request times out.

Testing procedure

• Check the new endpoint works and returns data as expected

Pre-requisites

Based on the Contributing Guidelines the PR author and the reviewers must check the following requirements are met:

• was the PR targeted to the correct branch?
• if this is a larger feature that probably needs more than one PR, is there a feat branch created?
• if this is a feat branch merging, do all satellite projects have a proper tag inside go.mod?