Combine `listitem` steps for installation and validation

[dan-snelson]

Note: While all requests are welcome, finding available cycles to custom-code a feature we won't use in our production environment is always challenging.

Is your feature request related to a problem? Please describe.
As pointed out by @roiegat on the Mac Admin's Slack #setup-yourmac Channel, combine listitem steps for installation and validation.

Describe the solution you'd like

Current:

policy_array=('
{
    "steps": [
        {
            "listitem": "Rosetta",
            "icon": "8bac19160fabb0c8e7bac97b37b51d2ac8f38b7100b6357642d9505645d37b52",
            "progresstext": "Rosetta enables a Mac with Apple silicon to use apps built for a Mac with an Intel processor.",
            "trigger_list": [
                {
                    "trigger": "rosettaInstall",
                    "validation": "None"
                }
            ]
        },
        {
            "listitem": "Rosetta Services (Local)",
            "icon": "8bac19160fabb0c8e7bac97b37b51d2ac8f38b7100b6357642d9505645d37b52",
            "progresstext": "Locally validating Rosetta service …",
            "trigger_list": [
                {
                    "trigger": "rosetta",
                    "validation": "Local"
                }
            ]
        },

Proposed:

policy_array=('
{
    "steps": [
        {
            "listitem": "Rosetta",
            "icon": "8bac19160fabb0c8e7bac97b37b51d2ac8f38b7100b6357642d9505645d37b52",
            "progresstext": "Rosetta enables a Mac with Apple silicon to use apps built for a Mac with an Intel processor.",
            "trigger_list": [
                {
                    "trigger": "rosettaInstall",
                    "validation": "None"
                },
                {
                    "trigger": "rosetta",
                    "validation": "Local"
                }
            ]
        },

[dan-snelson]

Addressed in 1.7.0.