[ML] Add a model memory estimation endpoint for anomaly detection (#53507)

A new endpoint for estimating anomaly detection job
model memory requirements:

POST _ml/anomaly_detectors/estimate_model_memory

Closes #53219

docs/java-rest/high-level/ml/estimate-model-memory.asciidoc

@@ -0,0 +1,42 @@
+--
+:api: estimate-model-memory
+:request: EstimateModelMemoryRequest
+:response: EstimateModelMemoryResponse
+--
+[role="xpack"]
+[id="{upid}-{api}"]
+=== Estimate {anomaly-job} model memory API
+
+Estimate the model memory an analysis config is likely to need for
+the given cardinality of the fields it references.
+
+[id="{upid}-{api}-request"]
+==== Estimate {anomaly-job} model memory request
+
+A +{request}+ can be set up as follows:
+
+["source","java",subs="attributes,callouts,macros"]
+--------------------------------------------------
+include-tagged::{doc-tests-file}[{api}-request]
+--------------------------------------------------
+<1> Pass an `AnalysisConfig` to the constructor.
+<2> For any `by_field_name`, `over_field_name` or
+    `partition_field_name` fields referenced by the
+    detectors, supply overall cardinality estimates
+    in a `Map`.
+<3> For any `influencers`, supply a `Map` containing
+    estimates of the highest cardinality expected in
+    any single bucket.
+
+include::../execution.asciidoc[]
+
+[id="{upid}-{api}-response"]
+==== Estimate {anomaly-job} model memory response
+
+The returned +{response}+ contains the model memory estimate:
+
+["source","java",subs="attributes,callouts,macros"]
+--------------------------------------------------
+include-tagged::{doc-tests-file}[{api}-response]
+--------------------------------------------------
+<1> The model memory estimate.

docs/java-rest/high-level/supported-apis.asciidoc

@@ -295,6 +295,7 @@ The Java High Level REST Client supports the following Machine Learning APIs:
 * <<{upid}-put-calendar-job>>
 * <<{upid}-delete-calendar-job>>
 * <<{upid}-delete-calendar>>
+* <<{upid}-estimate-model-memory>>
 * <<{upid}-get-data-frame-analytics>>
 * <<{upid}-get-data-frame-analytics-stats>>
 * <<{upid}-put-data-frame-analytics>>
@@ -351,6 +352,7 @@ include::ml/delete-calendar-event.asciidoc[]
 include::ml/put-calendar-job.asciidoc[]
 include::ml/delete-calendar-job.asciidoc[]
 include::ml/delete-calendar.asciidoc[]
+include::ml/estimate-model-memory.asciidoc[]
 include::ml/get-data-frame-analytics.asciidoc[]
 include::ml/get-data-frame-analytics-stats.asciidoc[]
 include::ml/put-data-frame-analytics.asciidoc[]