chore(web): consistent usage of the intial state context

[JGAntunes]

What this PR does / why we need it:

Quick cleanup of the initial state context component:

• Renamed it from Branding* to what it actually is (Initial State)
• Added some types and type guards
• Use the InitialStateContext everywhere instead of accessing window.* directly.
• Some tests
• Some type cleanups.

Which issue(s) this PR fixes:

NA

Does this PR require a test?

Adds tests

Does this PR require a release note?

NONE

Does this PR require documentation?

NONE

[diamonwiggins]

lgtm

[github-actions]

This PR has been released (on staging) and is available for download with a embedded-cluster-smoke-test-staging-app license ID.

Online Installer:

curl "https://staging.replicated.app/embedded/embedded-cluster-smoke-test-staging-app/ci/appver-dev-5337789" -H "Authorization: $EC_SMOKE_TEST_LICENSE_ID" -o embedded-cluster-smoke-test-staging-app-ci.tgz

Airgap Installer (may take a few minutes before the airgap bundle is built):

curl "https://staging.replicated.app/embedded/embedded-cluster-smoke-test-staging-app/ci-airgap/appver-dev-5337789?airgap=true" -H "Authorization: $EC_SMOKE_TEST_LICENSE_ID" -o embedded-cluster-smoke-test-staging-app-ci.tgz

Happy debugging!