[DOCS] Adds peak_model_bytes and assignment_memory_basis to GET model snapshot API docs (#75413)

docs/reference/ml/anomaly-detection/apis/get-snapshot.asciidoc

@@ -97,6 +97,10 @@ properties:
 .Properties of `model_size_stats`
 [%collapsible%open]
 ====
+`assignment_memory_basis`:::
+(string)
+include::{es-repo-dir}/ml/ml-shared.asciidoc[tag=assignment-memory-basis]
+
 `bucket_allocation_failures_count`:::
 (long) The number of buckets for which entities were not processed due to memory
 limit constraints.
@@ -164,6 +168,10 @@ reclaim space.
 `model_bytes_memory_limit`:::
 (long) The upper limit for memory usage, checked on increasing values.
 
+`peak_model_bytes`:::
+(long) The highest recorded value for the model memory usage.
+
+
 `rare_category_count`:::
 (long) The number of categories that match just one categorized document.