docs: Update IAVSRegistar in docs/core/AllocationManager.md

[HudsonGraeme]

Motivation:

The IAVSRegistrar interface has diverged from the documented interface within docs/core/AllocationManager.md. While implementing IAVSRegistrar following the document, this divergence was discovered. The goal of this PR is to address the divergence by bringing the relevant document up to date with the code implementation.

Modifications:

The docs/core/AllocationManager.md file is updated to correctly reflect the current state of IAVSRegistrar.

Result:

The documentation for AllocationManager.md now reflects the current implementation of IAVSRegistrar.

[HudsonGraeme]

A minor thought here too, to reduce future efforts needed to keep docs in sync with code changes. It may prudent to consider only linking to the relevant code sections, rather than including the code blocks themselves within the docs.

[non-fungible-nelson]

@MadelineAu - for consideration and merging into repo