[Fleet] adding object_type for fields under a group (#162041)

## Summary

Relates https://github.com/elastic/kibana/issues/155004

Fixes a limitation that wildcard fields under a group field were not
changed to `type:object` with `object_type`.

This was discovered during testing with prometheus package where a field
was changed to `type:double` and it was not converted to object type:
c17d59c887/packages/prometheus/data_stream/collector/fields/fields.yml (L9)

To verify, upload the package
[prometheus-1.5.2.zip](12069089/prometheus-1.5.2.zip)
and verify that the resulting `collector` and `remote_write` `@package`
component template has `prometheus.metrics.*` in `dynamic_templates`
```
curl -XPOST -H 'content-type: application/zip' -H 'kbn-xsrf: true' http://localhost:5601/julia/api/fleet/epm/packages -u elastic:changeme --data-binary @prometheus-1.5.2.zip
```
<img width="499" alt="image"
src="337295d8-9e3c-40c8-8b13-bda6229e7272">

### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

x-pack/plugins/fleet/server/services/epm/fields/field.test.ts

@@ -671,6 +671,60 @@ describe('processFields', () => {
     `);
   });
 
+  test('handle wildcard field inside group', () => {
+    const wildcardFields = [
+      {
+        name: 'prometheus',
+        type: 'group',
+        fields: [
+          {
+            name: 'metrics.*',
+            type: 'double',
+            metric_type: 'gauge',
+          },
+          {
+            name: 'child_group',
+            type: 'group',
+            fields: [
+              {
+                name: 'child.*',
+                type: 'double',
+                metric_type: 'gauge',
+              },
+            ],
+          },
+        ],
+      },
+    ];
+
+    expect(processFieldsWithWildcard(wildcardFields)).toEqual([
+      {
+        name: 'prometheus',
+        type: 'group',
+        fields: [
+          {
+            name: 'metrics.*',
+            type: 'object',
+            object_type: 'double',
+            metric_type: 'gauge',
+          },
+          {
+            name: 'child_group',
+            type: 'group',
+            fields: [
+              {
+                name: 'child.*',
+                type: 'object',
+                object_type: 'double',
+                metric_type: 'gauge',
+              },
+            ],
+          },
+        ],
+      },
+    ]);
+  });
+
   describe('processFieldsWithWildcard', () => {
     const wildcardWithObjectTypeYml = `
     - name: a.*.b

x-pack/plugins/fleet/server/services/epm/fields/field.ts

@@ -257,7 +257,11 @@ export function processFieldsWithWildcard(fields: Fields): Fields {
   const newFields: Fields = [];
   for (const field of fields) {
     const objectTypeField = processFieldWithoutObjectType(field);
-    newFields.push({ ...objectTypeField });
+    // adding object_type for fields under a group type
+    if (objectTypeField.type === 'group' && objectTypeField.fields) {
+      objectTypeField.fields = processFieldsWithWildcard(objectTypeField.fields);
+    }
+    newFields.push(objectTypeField);
   }
   return newFields;
 }
@@ -265,7 +269,7 @@ export function processFieldsWithWildcard(fields: Fields): Fields {
 export function processFieldWithoutObjectType(field: Field): Field {
   const hasWildcard = field.name.includes('*');
   const hasObjectType = field.object_type;
-  if (hasWildcard && !hasObjectType) {
+  if (hasWildcard && !hasObjectType && field.type !== 'object') {
     return { ...field, type: 'object', object_type: field.type };
   } else {
     return { ...field };