[Fleet] Fix error with creating agent policy during add integration

[jen-huang]

Summary

Fixes #83990. With at least one agent enrolled in Default policy, trying to create a new agent policy during Add integration throws an error. After I fixed that, another issue came up where Saving the integration would give the "Save and deploy changes" modal, even though the newly created policy does not have any agents enrolled yet.

This PR fixes both of those issues. I cleaned up some eslint-disable-next-line too while I was in the area.

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[jen-huang]

@elasticmachine merge upstream

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: d54e030

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
fleet	1.1MB	1.1MB	+525.0B

History

• 💚 Build #89409 succeeded 2923f42

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[nchaulet]

👍

[ghost]

Hi @jen-huang

We have validated this ticket on 7.10.1 BC1 Kibana cloud environment(deployed from staging platform) with 7.10.1 BC1 Windows x64 agent and found it fixed.

Build details:
Kibana Commit: 1d4cfde288ede0c4bc6277b4d589ca0cb96b231f
Build : 36050
7.10.1 BC1 Windows x64 agent package link: https://staging.elastic.co/7.10.1-ce3b40e6/downloads/beats/elastic-agent/elastic-agent-7.10.1-windows-x86_64.zip

Prerequisite:

1. 'elastic' superuser should be logged-in to 7.10.1 BC1 kibana cloud environment.
2. 7.10.1 BC1 Windows x64 agent should be installed(using './elastic-agent install' command) with Default policy.

Steps followed:

1. Click on left hand 'Fleet' link and navigate to Integrations tab

2. Click on 'System' integration and navigate to its detail page.

3. Click on 'Add System' link and navigate to 'Add System integration' detail page.

4. Click on 'Create new agent policy' link.

5. Provide new policy name(say rahul_new_policy) having no agents enrolled and unselect 'Collect system metrics' checkbox on 'Create agent policy' flyout.

6. Click on 'Create agent policy' button and observe that "Agent policy 'rahul_new_policy' created" toast message is successfully displayed with no errors.
   Screenshot:
   

7. Click on 'Save integration' button and observe that "Save and deploy changes" modal is not displayed and system integration is added in 'rahul_new_policy' policy.
   Screenshot:
   

Hence, we are closing this bug.