refactor: move agent initialization into a hook, tidy migration check

[bryce-mcmath]

Summary of Changes

1) Move the agent initialization logic from the splash screen into a hook and export said hook 2) Get rid of unnecessary async function wrapper for onboarding useEffect in splash screen 3) Clean up didMigrateToAskar logic and remove unneeded code

Related Issues

N/A

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[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud