feat: add feature flag to disable platform

[FrederikBolding]

Add getFeatureFlags constructor argument that can return dynamic feature flags at runtime, use the feature flag to assert whether the Snaps platform is allowed to run.

Closes https://github.com/MetaMask/MetaMask-planning/issues/2556

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.30%. Comparing base (10a9f79) to head (04ad368).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2434 +/- ## ======================================= Coverage 94.30% 94.30% ======================================= Files 437 437 Lines 8987 8997 +10 Branches 1378 1379 +1 ======================================= + Hits 8475 8485 +10 Misses 512 512 ```

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