Migrate auth-related methods from ResourceManager to CCloud auth provider

## Problem

The `ResourceManager` class currently contains several authentication-related methods that don't align with its primary responsibility of managing resource caching and storage. These methods are more appropriately placed in the CCloud auth provider class or dedicated auth helper functions.

## Current Implementation

The following auth-related methods are currently in `ResourceManager`:

https://github.com/confluentinc/vscode/blob/5875a68d3702604f740977bd1f05285d8db4e89b/src/storage/resourceManager.ts#L634-L672

- `setAuthFlowCompleted(authCallback: AuthCallbackEvent)`
- `getAuthFlowCompleted()`
- `getAuthFlowPasswordReset()`
- `setCCloudAuthStatus(status: Status)`
- `getCCloudAuthStatus()`

## Proposed Solution

Move these methods to a more appropriate location:

1. **Option 1**: Migrate to the existing CCloud auth provider class
2. **Option 2**: Create dedicated auth helper functions/utilities

The methods should maintain their current functionality but be logically grouped with other authentication-related code.

## Benefits

- **Single Responsibility**: `ResourceManager` can focus solely on resource caching and management
- **Better Organization**: Auth-related functionality is co-located with other auth code
- **Improved Maintainability**: Easier to find and modify auth-related storage logic
- **Cleaner Architecture**: More logical separation of concerns

## Acceptance Criteria

- [ ] Auth methods are moved from `ResourceManager` to appropriate auth-related class/module
- [ ] All existing functionality is preserved
- [ ] All callers of these methods are updated to use the new location
- [ ] Unit tests are updated to reflect the new structure

## Implementation Notes

- Ensure proper handling of VS Code's `SecretStorage` API
- Maintain existing error handling patterns
- Consider any dependencies on the current `ResourceManager` mutex/locking mechanisms
- Update imports across the codebase as needed