feat: query multiple identity balances

[QuantumExplorer]

Issue being fixed or feature implemented

Currently there is no easy way except many many requests to get multiple identity balances. This PR tries to remedy this situation.

What was done?

Added a new query for multiple identity balances.

How Has This Been Tested?

(Todo: add SDK tests)

Breaking Changes

Not breaking.

Checklist:

• [X] I have performed a self-review of my own code
• [X] I have commented my code, particularly in hard-to-understand areas
• [X] I have added or updated relevant unit/integration/functional/e2e tests
• [X] I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• [X] I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• [ ] I have assigned this pull request to a milestone