Add instanceprincipal clusteridentity support

[shyamradhakrishnan]

What this PR does / why we need it:

Add InstancePrincipal support to ClusterIdentity.

Just as an add on, some other cloud provider are also moving away from env variable based identity to use Cluster Identity. So this will help us to be on par.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #314

[shyamradhakrishnan]

unit test

GOBIN=/home/ubuntu/go/src/github.com/oracle/cluster-api-provider-oci/hack/tools/bin ./scripts/go_install.sh sigs.k8s.io/controller-runtime/tools/setup-envtest setup-envtest v0.0.0-20230131074648-f5014c077fc3
kube-builder assets: /home/ubuntu/.local/share/kubebuilder-envtest/k8s/1.24.2-linux-amd64
KUBEBUILDER_ASSETS="/home/ubuntu/.local/share/kubebuilder-envtest/k8s/1.24.2-linux-amd64" go test -coverprofile=coverage.out ./...
?   	github.com/oracle/cluster-api-provider-oci	[no test files]
ok  	github.com/oracle/cluster-api-provider-oci/api/v1beta1	58.251s	coverage: 23.7% of statements
ok  	github.com/oracle/cluster-api-provider-oci/api/v1beta2	0.094s	coverage: 15.7% of statements
?   	github.com/oracle/cluster-api-provider-oci/cloud/config	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/metrics	[no test files]
ok  	github.com/oracle/cluster-api-provider-oci/cloud/ociutil	0.004s	coverage: 19.6% of statements
ok  	github.com/oracle/cluster-api-provider-oci/cloud/scope	241.063s	coverage: 75.0% of statements
?   	github.com/oracle/cluster-api-provider-oci/cloud/scope/mocks	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/base	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/base/mock_base	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/compute	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/compute/mock_compute	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/computemanagement	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/computemanagement/mock_computemanagement	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/containerengine	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/containerengine/mock_containerengine	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/identity	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/identity/mock_identity	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/loadbalancer	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/loadbalancer/mock_lb	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/networkloadbalancer	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/networkloadbalancer/mock_nlb	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/vcn	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/vcn/mock_vcn	[no test files]
ok  	github.com/oracle/cluster-api-provider-oci/cloud/util	0.139s	coverage: 73.4% of statements
ok  	github.com/oracle/cluster-api-provider-oci/controllers	27.030s	coverage: 60.3% of statements
ok  	github.com/oracle/cluster-api-provider-oci/exp/api/v1beta1	14.292s	coverage: 15.2% of statements
ok  	github.com/oracle/cluster-api-provider-oci/exp/api/v1beta2	0.016s	coverage: 4.8% of statements
ok  	github.com/oracle/cluster-api-provider-oci/exp/controllers	0.435s	coverage: 58.4% of statements
?   	github.com/oracle/cluster-api-provider-oci/feature	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/version	[no test files]

[shyamradhakrishnan]

e2e tests

Ran 7 of 28 Specs in 3681.027 seconds
SUCCESS! -- 7 Passed | 0 Failed | 0 Pending | 21 Skipped

[joekr]

super small change.

Does this change mean we now need to run our e2e tests within OCI and not on local machines or (in the future) prow? Since the managed virtual test uses instance principal?