feat: add InstancePools to EndpointConfig ProductionVariants

[michaelhtm]

Description of changes:
Bumps the sagemaker SDK to v1.244.0 to expose the InstancePools field on
ProductionVariant, enabling heterogeneous endpoints that provision across a
prioritized list of instance types. The field maps automatically as a nested
field on the already-generated ProductionVariant shape; no hooks needed.

The SDK bump also introduces unrelated new resources and fields. To keep the
change scoped to InstancePools, new resources (AIBenchmarkJob,
AIRecommendationJob, AIWorkloadConfig, MlflowApp, PresignedMlflowAppUrl) are
added to ignore.resource_names, and new out-of-scope fields (MetricsConfig,
Specifications, ScaleInPolicy, DataCacheConfig, SchedulingConfig,
ModelPackageRegistrationType, AdditionalModelDataSources, BaseModel,
DatasetSource, MlflowConfig, ModelPackageConfig, ServerlessJobConfig,
VariantInstanceProvisionTimeoutInSeconds, MlflowExperimentName, and others)
are added to ignore.field_paths on both their input and output shapes.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[ack-prow]

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[michaelhtm]

/label release/minor