fix: Add useMultiRpcMigration to PreferencesController

[salimtb]

Explanation

Current state:
The PreferencesController does not include support for two new features related to network validation and multi-RPC migration behavior. Specifically, there is no existing functionality to:

1. Control the display of the multi-RPC migration modal (useMultiRpcMigration).

Solution:
This PR adds two new properties to the PreferencesController state:

• useMultiRpcMigration: Controls whether the multi-RPC migration modal is displayed.

Along with these additions, corresponding setter methods ( setUseMultiRpcMigration) have been implemented. These methods allow for toggling the state of the new properties.

Additional details:

• Test cases have been added to ensure that the new properties are correctly updated in the state when their respective setter methods are invoked.
• The default values for these properties have been set to true to maintain expected functionality for users.

There were no additional package updates or dependency changes required in this PR.

References

• No specific issues or pull requests tied to this change.

Changelog

@metamask/preferences-controller

• ADDED: Added useMultiRpcMigration property to the PreferencesController state, controlling the display of the multi-RPC migration modal.
• ADDED: Implemented setUseMultiRpcMigration method to toggle the useMultiRpcMigration property.

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've highlighted breaking changes using the "BREAKING" category above as appropriate
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes (N/A)