Bump controller-runtime to v0.8.0

[coro]

Replacement PR for #564

Controller-runtime v0.8.0 bumps k8s dependencies to v1.20 of the k8s API, which includes breaking changes to the ServiceSpec object. While we don't set these fields in our operator, the unit tests do as part of the override functionality, hence the need to both bump & fix tests.

Note to reviewers: remember to look at the commits in this PR and consider if they can be squashed

Local Testing

Please ensure you run the unit, integration and system tests before approving the PR.

To run the unit and integration tests:

$ make unit-tests integration-tests

You will need to target a k8s cluster and have the operator deployed for running the system tests.

For example, for a Kubernetes context named dev-bunny:

$ kubectx dev-bunny
$ make destroy deploy-dev
# wait for operator to be deployed
$ make system-tests

[ferozjilla]

LGTM

[ChunyiLyu]

Great!