network-controller: Mention addition of degraded status in changelog (#7293)

## Explanation

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In 5d24e81, `degraded` was added as a
new property of the `NetworkStatus` enum. This fact was not properly
noted in the changelog, so this commit retroactively adds a changelog
entry.

## References

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## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [x] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [x] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/contributing.md#updating-changelogs)
- [x] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Updates CHANGELOG to document that `networksMetadata` can include a
`degraded` network status.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
116659f. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: mcmire

packages/network-controller/CHANGELOG.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Add `NetworkController:rpcEndpointChainAvailable` messenger event ([#7166](https://github.com/MetaMask/core/pull/7166))
   - This is a counterpart to the (new) `NetworkController:rpcEndpointChainUnavailable` and `NetworkController:rpcEndpointChainDegraded` events, but is published when a successful request to an endpoint within a chain of endpoints is made either initially or following a previously established degraded or unavailable status.
+- Update `networksMetadata` state property so that networks can now have a possible status of `degraded` ([#7186](https://github.com/MetaMask/core/pull/7186))
 
 ### Changed