chore(similarity): Move feature flags to list not used in FE

[jangjodi]

Add similarity feature flags to list of flags not used in the frontend This will prevent them from being serialized in project index endpoint, which is slow for the similarity-embeddings flag

[codecov[bot]]

:x: 876 Tests Failed:

Tests completed	Failed	Passed	Skipped
23115	876	22239	215

View the top 3 failed tests by shortest run time

> > ```python > tests.sentry.users.api.endpoints.test_user_details.UserDetailsSuperuserUpdateTest::test_superuser_with_permission_can_change_is_active > ``` > >

Stack Traces | 0.005s run time

> > > > > ```python > > No failure message available > > ``` > >

tests.sentry.users.web.test_accounts.TestAccounts::test_confirm_email_invalid_hash

Stack Traces | 0.005s run time

> > ```python > No failure message available > ```

tests.sentry.sentry_apps.test_sentry_app_creator.TestCreator::test_creates_proxy_user

Stack Traces | 0.006s run time

> > ```python > No failure message available > ```

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