feat: determine network interface / IP on join

[sgalsaleh]

What this PR does / why we need it:

• Automatically determines the network interfaces on join.
• Fixes an issue where the internal node IP wasn't set from the user-specified network interface.

Which issue(s) this PR fixes:

Does this PR require a test?

Does this PR require a release note?

Does this PR require documentation?

NONE

[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-3dc436a" -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-3dc436a?airgap=true" -H "Authorization: $EC_SMOKE_TEST_LICENSE_ID" -o embedded-cluster-smoke-test-staging-app-ci.tgz

Happy debugging!