Rename root-certificate to brupop-selfsigned-ca

[alekhrycaiko]

Issue number:

https://github.com/bottlerocket-os/bottlerocket-update-operator/issues/486

Description of changes:

This attempts to address #486.

Changes root certificate referenced based on current findings of the issue.

Testing done:

Ran test suite.

Our own cluster already relies on brupop-selfsigned-ca. But I have not ran this specific PR against the cluster and could use an additional verification/eye there.

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.