Document default search technique change for Options List controls

The default search technique for newly created Options List controls changed
from Prefix to Contains in 9.4 (Kibana PR #250992). Add search technique
options to the 9.4 tab (were missing) with Contains as default, and mark
Prefix as default in the 9.0-9.3 tab.

Closes #4951

Author: florent-leborgne

explore-analyze/dashboards/add-controls.md

@@ -75,6 +75,13 @@ To add interactive Options list and Range slider controls, create the controls,
     * **Label**: Overwrite the default field name with a clearer and self-explanatory label.
     - **Selections**:
       Select multiple values to filter with the control, or only one.
+    - **Search technique** (for Options list controls on *string* and *IP address* type fields):
+
+      * **Prefix**: Show options that *start with* the entered value.
+      * **Contains** (default): Show options that *contain* the entered value. This setting is only available for *string* type fields.
+      * **Exact**: Show options that are an *exact* match with the entered value.
+
+      The search is not case sensitive. For example, searching for `ios` would still retrieve `iOS` if that value exists.
     - **Additional settings**:
 
       - **Use global filters**: A panel-level setting that applies to each individual control. It is enabled by default.
@@ -96,8 +103,8 @@ To add interactive Options list and Range slider controls, create the controls,
 
       For Options list controls on *string* and *IP address* type fields, you can define how the control’s embedded search should behave:
 
-      * **Prefix**: Show options that *start with* the entered value.
-      * **Contains**: Show options that *contain* the entered value. This setting option is only available for *string* type fields. Results can take longer to show with this option.
+      * **Prefix** (default): Show options that *start with* the entered value.
+      * **Contains**: Show options that *contain* the entered value. This setting is only available for *string* type fields.
       * **Exact**: Show options that are an *exact* match with the entered value.
 
       The search is not case sensitive. For example, searching for `ios` would still retrieve `iOS` if that value exists.