Read by index rpc

MERGE REQUEST

Overview

This MR adds another Read RPC which is able to partially read sectors by index instead of by root.

Changes to Work Flow

Pretty much the same as the other Read RPC except that the host looks up the merkle root by index and returns the merkle root for the renter to verify the proof.

Testing Changes

extended TestSession

Documentation Changes

N/A

Modules and Packages Impacted

modules/host, modules/renter/proto, siatest/renterhost

Example for Visual changes (ie Screenshot)

N/A

Issues Closed

N/A

Checklist

Review and complete the checklist to ensure that the MR is complete before assigned to an approver.

• Pipeline Passing (this is for NDFs where tests were run in a loop)
• All new methods, or updating methods have clear docstrings
• Testing added or updated for new methods
• API documentation updated for API updates
• Module README.md updated for changes to work flow
• Issue added to Sia-UI repo for new supporting features