Add getDiff to client rest module

[joneubank]

Description

Add to client ability to fetch diff between two versions of a dictionary

Type of change

Please choose only the relevant options and remove the others.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration.

• Manual testing of client through REPL

Checklist:

You do not need to fullfill all requirements of this checklist, select all that apply:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

Additional context

Follows established pattern of existing client rest functions.

[leoraba]

LGTM