make new variables optional (#7521)

## Explanation

The `localOverrides` and `rawRemoteFeatureFlags` properties were
recently added to `RemoteFeatureFlagControllerState` in PR #7271 as
required properties. However, consumers with existing persisted state
from before these properties were added will experience TypeScript
errors when their state is loaded, since these properties won't exist in
the persisted data but are marked as required.

This PR marks `localOverrides` and `rawRemoteFeatureFlags` as optional
in the `RemoteFeatureFlagControllerState` type to ensure backwards
compatibility with existing persisted state. The
`getDefaultRemoteFeatureFlagControllerState()` function continues to
initialize these properties with empty objects, so newly created state
will still have them populated.

## References

- Related to #7271

## 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)
- [ ] 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

Author: asalsys

packages/remote-feature-flag-controller/src/remote-feature-flag-controller.ts

@@ -28,8 +28,8 @@ export const DEFAULT_CACHE_DURATION = 24 * 60 * 60 * 1000; // 1 day
 
 export type RemoteFeatureFlagControllerState = {
   remoteFeatureFlags: FeatureFlags;
-  localOverrides: FeatureFlags;
-  rawRemoteFeatureFlags: FeatureFlags;
+  localOverrides?: FeatureFlags;
+  rawRemoteFeatureFlags?: FeatureFlags;
   cacheTimestamp: number;
 };