Allow integrations of hosted policies to be updated (#96705)

## Summary

Remove the restriction against updating integrations on hosted policies.

I described the current behavior and asked if it should change in [1]. Based on the responses in [2] & [3] and looking back at prior discussion around hosted policies, I don't think updates should be restricted.

Adding or removing integrations is still blocked for hosted policies. Updated API tests to confirm behavior. 


[1] #76843 (comment)
[2] #76843 (comment)
[3] #76843 (comment)

## Screenshots
<details><summary>Current behavior</summary>

<h3>Error about updating integrations of a managed policy</h3>

<img width="1208" alt="Screen Shot 2021-04-08 at 3 23 37 PM" src="https://user-images.githubusercontent.com/57655/114084750-87686880-987e-11eb-91a9-081c45dbe871.png">

<details><summary>via flow A</summary>
<img width="1223" alt="Screen Shot 2021-04-08 at 3 01 32 PM" src="https://user-images.githubusercontent.com/57655/114082826-3a839280-987c-11eb-94d0-151ae93ab523.png">

<img width="1205" alt="Screen Shot 2021-04-08 at 3 13 24 PM" src="https://user-images.githubusercontent.com/57655/114083728-5c314980-987d-11eb-92be-195d7d44c037.png">
</details>

<details><summary>via flow B</summary>
<img width="1221" alt="Screen Shot 2021-04-08 at 3 19 52 PM" src="https://user-images.githubusercontent.com/57655/114084502-3fe1dc80-987e-11eb-8879-57718586ac95.png">
<img width="1198" alt="Screen Shot 2021-04-08 at 3 20 06 PM" src="https://user-images.githubusercontent.com/57655/114084503-3fe1dc80-987e-11eb-9fa9-512210b938cd.png">
</details>

</details>

<details><summary>This PR</summary>
<h3>Successful updates using either form</h3>
<img width="1301" alt="Screen Shot 2021-04-09 at 1 21 02 PM" src="https://user-images.githubusercontent.com/57655/114219370-8f84de80-9938-11eb-9b94-dfbeb18535b2.png">
<img width="1320" alt="Screen Shot 2021-04-09 at 1 05 10 PM" src="https://user-images.githubusercontent.com/57655/114219408-9f9cbe00-9938-11eb-96d2-2918332d1539.png">

</details>


### 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

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

x-pack/plugins/fleet/server/services/package_policy.ts

@@ -316,18 +316,14 @@ class PackagePolicyService {
     const parentAgentPolicy = await agentPolicyService.get(soClient, packagePolicy.policy_id);
     if (!parentAgentPolicy) {
       throw new Error('Agent policy not found');
-    } else {
-      if (parentAgentPolicy.is_managed) {
-        throw new IngestManagerError(`Cannot update integrations of managed policy ${id}`);
-      }
-      if (
-        (parentAgentPolicy.package_policies as PackagePolicy[]).find(
-          (siblingPackagePolicy) =>
-            siblingPackagePolicy.id !== id && siblingPackagePolicy.name === packagePolicy.name
-        )
-      ) {
-        throw new Error('There is already a package with the same name on this agent policy');
-      }
+    }
+    if (
+      (parentAgentPolicy.package_policies as PackagePolicy[]).find(
+        (siblingPackagePolicy) =>
+          siblingPackagePolicy.id !== id && siblingPackagePolicy.name === packagePolicy.name
+      )
+    ) {
+      throw new Error('There is already a package with the same name on this agent policy');
     }
 
     let inputs = restOfPackagePolicy.inputs.map((input) =>

x-pack/test/fleet_api_integration/apis/package_policy/update.ts

@@ -4,7 +4,6 @@
  * 2.0; you may not use this file except in compliance with the Elastic License
  * 2.0.
  */
-import expect from '@kbn/expect';
 import { FtrProviderContext } from '../../../api_integration/ftr_provider_context';
 import { skipIfNoDockerRegistry } from '../../helpers';
 
@@ -115,15 +114,15 @@ export default function (providerContext: FtrProviderContext) {
       await getService('esArchiver').unload('empty_kibana');
     });
 
-    it('should fail on managed agent policies', async function () {
-      const { body } = await supertest
+    it('should work with valid values on "regular" policies', async function () {
+      await supertest
         .put(`/api/fleet/package_policies/${packagePolicyId}`)
         .set('kbn-xsrf', 'xxxx')
         .send({
           name: 'filetest-1',
           description: '',
           namespace: 'updated_namespace',
-          policy_id: managedAgentPolicyId,
+          policy_id: agentPolicyId,
           enabled: true,
           output_id: '',
           inputs: [],
@@ -132,21 +131,18 @@ export default function (providerContext: FtrProviderContext) {
             title: 'For File Tests',
             version: '0.1.0',
           },
-        })
-        .expect(400);
-
-      expect(body.message).to.contain('Cannot update integrations of managed policy');
+        });
     });
 
-    it('should work with valid values', async function () {
+    it('should work with valid values on hosted policies', async function () {
       await supertest
         .put(`/api/fleet/package_policies/${packagePolicyId}`)
         .set('kbn-xsrf', 'xxxx')
         .send({
           name: 'filetest-1',
           description: '',
           namespace: 'updated_namespace',
-          policy_id: agentPolicyId,
+          policy_id: managedAgentPolicyId,
           enabled: true,
           output_id: '',
           inputs: [],