Adjust metrics top menu layout to avoid overflow (opensearch-project#398)

Signed-off-by: Joshua Li <joshuali925@gmail.com>

Author: joshuali925

public/components/metrics/sidebar/__tests__/__snapshots__/searchbar.test.tsx.snap

@@ -15,7 +15,9 @@ exports[`Search Bar Component Search Side Bar Component with available metrics 1
   <Component
     setSearch={[MockFunction]}
   >
-    <div>
+    <div
+      className="metrics-search-bar-input"
+    >
       <EuiSearchBar
         box={
           Object {
@@ -164,7 +166,9 @@ exports[`Search Bar Component Search Side Bar Component with no available metric
   <Component
     setSearch={[MockFunction]}
   >
-    <div>
+    <div
+      className="metrics-search-bar-input"
+    >
       <EuiSearchBar
         box={
           Object {

public/components/metrics/sidebar/search_bar.tsx

@@ -28,7 +28,7 @@ export const SearchBar = (props: ISearchBarProps) => {
   };
 
   return (
-    <div>
+    <div className="metrics-search-bar-input">
       <EuiSearchBar
         box={{
           placeholder: 'Search for metrics',