Don't assume order and length is the same between observed and predicted features

Summary:
Combining diffs D68274239 & D68294872:

1 - **D68274239 - [analysis] Don't assume order is the same in observed and predicted features**

This is causing only 3 of 14 arms to show on an experiment.  We're still assuming that within an observation the order of the metric names matches the order of the corresponding data.

2 - **D68294872 - [analysis] Don't assume observed and predicted metrics are the same length**

Comment from  [here](https://www.internalfb.com/diff/D68274239?dst_version_fbid=9435339503152040&transaction_fbid=1415387593232440):

In N6432597 I encounter a `StopIteration` error when rebased on D68274239. I believe this is because `predicted.metric_names` is quite a bit longer than `observed.data.metric_names` and so there's a chance that

```
predicted_i = next(
            i
            for i in range(len(observed.data.metric_names))
            if predicted.metric_names[i] == metric_name
        )
```

never finds the metric it needs and throws the `StopIteration` error.

Differential Revision: D68336952

Author: eonofrey

ax/analysis/plotly/cross_validation.py

@@ -161,25 +161,30 @@ def _prepare_data(
                     f"trial {trial_index}, but has observations from trial "
                     f"{observed.features.trial_index}."
                 )
-        for i in range(len(observed.data.metric_names)):
-            # Find the index of the metric we want to plot
-            if not (
-                observed.data.metric_names[i] == metric_name
-                and predicted.metric_names[i] == metric_name
-            ):
-                continue
-
+        # Find the index of the metric in observed and predicted
+        observed_i = next(
+            (
+                i
+                for i, name in enumerate(observed.data.metric_names)
+                if name == metric_name
+            ),
+            None,
+        )
+        predicted_i = next(
+            (i for i, name in enumerate(predicted.metric_names) if name == metric_name),
+            None,
+        )
+        # Check if both indices are found
+        if observed_i is not None and predicted_i is not None:
             record = {
                 "arm_name": observed.arm_name,
-                "observed": observed.data.means[i],
-                "predicted": predicted.means[i],
-                # Take the square root of the the SEM to get the standard deviation
-                "observed_sem": observed.data.covariance[i][i] ** 0.5,
-                "predicted_sem": predicted.covariance[i][i] ** 0.5,
+                "observed": observed.data.means[observed_i],
+                "predicted": predicted.means[predicted_i],
+                # Take the square root of the SEM to get the standard deviation
+                "observed_sem": observed.data.covariance[observed_i][observed_i] ** 0.5,
+                "predicted_sem": predicted.covariance[predicted_i][predicted_i] ** 0.5,
             }
             records.append(record)
-            break
-
     return pd.DataFrame.from_records(records)