DAL: Refactor DAL rpc endpoints encodings to bytes

Context

It is important we are not returning or receiving data encoded as string when working with general/abstract payload. The reason for it is that there are many byte sequences that do not correspond to the valid UTF-8 string (important for correct JSON parsing). This MR changes some of the expected encodings of DAL RPC endpoints accordingly.

Closes #4120 (closed)

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR