[APM] Use form label for Transaction type selector (#28322) (#28478)

* Use form label for type selector

Removes the inline copy for filtering by transaction type and uses the FormRow label as a substitute.

* [APM] Updated test snapshot

x-pack/plugins/apm/public/components/app/TransactionOverview/__jest__/__snapshots__/TransactionOverview.test.js.snap

@@ -6,6 +6,7 @@ exports[`TransactionOverviewView should render with type filter controls 1`] = `
     describedByIds={Array []}
     fullWidth={false}
     hasEmptyLabelSpace={false}
+    label="Filter by type"
   >
     <EuiSelect
       compressed={false}
@@ -16,11 +17,11 @@ exports[`TransactionOverviewView should render with type filter controls 1`] = `
       options={
         Array [
           Object {
-            "text": "Filter by type: a",
+            "text": "a",
             "value": "a",
           },
           Object {
-            "text": "Filter by type: b",
+            "text": "b",
             "value": "b",
           },
         ]

x-pack/plugins/apm/public/components/app/TransactionOverview/index.tsx

@@ -48,10 +48,10 @@ export class TransactionOverviewView extends React.Component<
     return (
       <React.Fragment>
         {serviceTransactionTypes.length > 1 ? (
-          <EuiFormRow>
+          <EuiFormRow label="Filter by type">
             <EuiSelect
               options={serviceTransactionTypes.map(type => ({
-                text: `Filter by type: ${type}`,
+                text: `${type}`,
                 value: type
               }))}
               value={transactionType}