Fix IPV6 machine pool validation

[mantis-toboggan-md]

Summary

Fixes #15793 - specifically #15793 (comment)

Occurred changes and/or fixed issues

This PR updates the ec2 networking component to update its validation status when first rendered.

Technical notes summary

validationChanged events are used to control the display of error icons in machine pool tabs, and disable the save button when machine pools report errors. ec2Networking needs to emit validationChanged events when first rendered, as ec2 pools can be added in what the UI interprets to be an error state.

Areas or cases that should be tested

1. Navigate to the cluster management list view, click "create" and select "amazon ec2"
2. Check "Enable IPv6" in the only machine pool
3. Click the plus icon in the machine pool tab component to add a machine pool.
4. The new pool should have "Enable IPv6" checked. Uncheck it.
5. An error banner should appear in the pool's networking section. An error icon should appear on the other pool's tab
6. Click the plus icon again to add a third pool
7. The third pool should have "Enable IPv6" checked and an error banner should be displayed in the networking section
8. Select one of the other two pools and verify that the third pool now has an error icon on its tab

Areas which could experience regressions

• create button should be disabled when the ipv6 machine pool errors are shown
• create button should be enabled when ipv6 machine pool errors are resolved and there are no other errors in the form

Screenshot/Video

Screen.Recording.2025-11-04.at.10.19.47.AM.mov

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