🐛clusterctl: fix public library inconsistencies

[fabriziopandini]

What this PR does / why we need it:
This PR fixes some inconsistencies in the clusterctl public library, so now all the objects implement a unique approach for injecting values (based on a variadic list of options)

Which issue(s) this PR fixes
rif #1729

/area clusterctl
/milestone v0.3.0
/assign @ncdc
/assign @vincepri

[k8s-ci-robot]

@fabriziopandini: You must be a member of the kubernetes-sigs/cluster-api-maintainers GitHub team to set the milestone. If you believe you should be able to issue the /milestone command, please contact your Cluster API Maintainers and have them propose you as an additional delegate for this responsibility.

In response to this:

What this PR does / why we need it:
This PR fixes some inconsistencies in the clusterctl public library, so now all the objects implement a unique approach for injecting values (based on a variadic list of options)

Which issue(s) this PR fixes
rif #1729

/area clusterctl
/milestone v0.3.0
/assign @ncdc
/assign @vincepri

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[vincepri]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fabriziopandini, vincepri

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