HOSTEDCP-1542: cmd/cluster: refactor to remove example fixtures

[stevekuznetsov]

The goal of this refactor is to reduce the complexity in the command-line tooling. Overall, the changes here remove duplicative structures that copied data around and co-locate the logic with the data, instead of first aggregating all data into one uber-structure and then conditionally acting on that structure. These refactors have a number of benefits:

• locality of behavior: in the past, it was very difficult if not impossible to determine where a value was used, as it would be bound to a flag in one package, copied around between container structs a couple of times, then have some generic logic act on the presence or absence of the value to e.g. change a field on the HostedCluster. Simply reading the generic logic was often not enough to understand what was going on, as many of the conditional branches in the example fixture code could only ever trigger for one specific platform, and you'd never know unless you traced how the example options uber-struct had its fields set in every provider.
• clear go-to-definition: as a knock-on effect of the above, now there's one structure that holds a command-line flag and it's trivial to use the LSP when determining where that flag is used and how
• composability: as exemplified in the KubeVirt NodePool code, we are able to compose commands as necessary. When commands re-use the same arguments with the same flags and the same validation logic, there's no need to copy things around and re-implement anything; by localizing flag binding, validation and option completion, we gain small, composable parts that we can use to build larger commands with

[openshift-ci-robot]

@stevekuznetsov: This pull request references HOSTEDCP-1542 which is a valid jira issue.

In response to this:

The goal of this refactor is to reduce the complexity in the command-line tooling. Overall, the changes here remove duplicative structures that copied data around and co-locate the logic with the data, instead of first aggregating all data into one uber-structure and then conditionally acting on that structure. These refactors have a number of benefits:

• locality of behavior: in the past, it was very difficult if not impossible to determine where a value was used, as it would be bound to a flag in one package, copied around between container structs a couple of times, then have some generic logic act on the presence or absence of the value to e.g. change a field on the HostedCluster. Simply reading the generic logic was often not enough to understand what was going on, as many of the conditional branches in the example fixture code could only ever trigger for one specific platform, and you'd never know unless you traced how the example options uber-struct had its fields set in every provider.
• clear go-to-definition: as a knock-on effect of the above, now there's one structure that holds a command-line flag and it's trivial to use the LSP when determining where that flag is used and how
• composability: as exemplified in the KubeVirt NodePool code, we are able to compose commands as necessary. When commands re-use the same arguments with the same flags and the same validation logic, there's no need to copy things around and re-implement anything; by localizing flag binding, validation and option completion, we gain small, composable parts that we can use to build larger commands with

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[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: stevekuznetsov
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[davidvossel]

kubevirt parts look accurate

[openshift-ci]

@stevekuznetsov: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/e2e-kubevirt-aws-ovn	b28e521	link	true	/test e2e-kubevirt-aws-ovn
ci/prow/e2e-azure	b28e521	link	false	/test e2e-azure
ci/prow/e2e-aws	b28e521	link	true	/test e2e-aws

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