Add a metric that will track prediction failures.

num_failed_inferences

``

Add metrics that track data on side loaded models

{}num_model_loads{}, {}num_model_versions{}, and curr_model_version

``

curr_model_version is less a metric and more of a static value. Part of this FR will be to figure out how that fits.

Imported from Jira BEAM-14043. Original Jira may contain additional context.
Reported by: Ryan.Thompson.
Subtask of issue #21435