feat: Add more MachinePool flexibility

[joekr]

What this PR does / why we need it:
This will now:

• keep track of machine pool instances in status
• variablize allowing public ips for the machine pool instances

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 #90

[joekr]

unit tests

?       github.com/oracle/cluster-api-provider-oci      [no test files]
ok      github.com/oracle/cluster-api-provider-oci/api/v1beta1  0.260s  coverage: 18.6% of statements
?       github.com/oracle/cluster-api-provider-oci/cloud/config [no test files]
ok      github.com/oracle/cluster-api-provider-oci/cloud/ociutil        0.712s  coverage: 25.0% of statements
ok      github.com/oracle/cluster-api-provider-oci/cloud/scope  176.165s        coverage: 73.9% of statements
?       github.com/oracle/cluster-api-provider-oci/cloud/scope/mocks    [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/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/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/controllers  26.302s coverage: 71.0% of statements
?       github.com/oracle/cluster-api-provider-oci/exp/api/v1beta1      [no test files]
?       github.com/oracle/cluster-api-provider-oci/exp/controllers      [no test files]
?       github.com/oracle/cluster-api-provider-oci/feature      [no test files]

e2e test

Ran 5 of 21 Specs in 1973.247 seconds
SUCCESS! -- 5 Passed | 0 Failed | 0 Pending | 16 Skipped