Multi Tiers upgrade new structure - part 1 - Business logic and API

[wordpressfan]

Is your feature request related to a problem? Please describe.
Part of this issue: https://github.com/wp-media/wp-rocket.me/issues/4326 we need to depend on the API from our website backend to show the upgrade section with generic blocks so we have the full control from the backend.

Describe the solution you'd like
As discussed with service team, we have a semi-final API contract here:
https://github.com/wp-media/wp-rocket.me/blob/9acee8e8d432d960a0fca8465319f6cd85a00198/openapi.yaml#L496-L524

So we have upgrades property in user API endpoint, so we will use this and prepare the list of upgrades details considering the stack property => if true, we will show them in the UI as select dropdown menu, exactly like what we have in our website new pricing page:

Here we need to agree on the data being passed to the UI view, I propose to have something like (the below example is for single license):

$choices = [
    'growth' => [
        'name' => 'Growth',
        'price' => '',
        'websites' => '',
        'upgrade_url' => '',
    ],
    'stacked' => [
        'multi10' => [
            'name' => 'Multi',
            'price' => '',
            'websites' => '',
            'upgrade_url' => '',
        ],
        'multi50' => [
            'name' => 'Multi',
            'price' => '',
            'websites' => '',
            'upgrade_url' => '',
        ],
        'multi100' => [
            'name' => 'Multi',
            'price' => '',
            'websites' => '',
            'upgrade_url' => '',
        ],
        'multi500' => [
            'name' => 'Multi',
            'price' => '',
            'websites' => '',
            'upgrade_url' => '',
        ],
    ]
];

We shouldn't have any static (hard-coded) values here.

Additional context
Slack discussion: https://wp-media.slack.com/archives/C0837DFAFEX/p1733383902203979

[remyperona]

This is in grooming to review, but there isn't any grooming done?

[MathieuLamiot]

@wordpressfan Can you update on this? Is there a grooming / the PR to review? Or is it grooming in progress? Or something else? Thanks

[wordpressfan]

@remyperona @MathieuLamiot

I mentioned the technical details in the issue itself and to make it easier I already started the PR to show the approach we will take also added the effort.
I was thinking of directly start working on it and continue on the mentioned PR and see how it goes.
Let me know if you think that detailed grooming is needed in this case.

[Mai-Saad]

Related initial test plan
https://wpmediaqa.testrail.io/index.php?/runs/view/941&group_by=cases:section_id&group_order=asc
(screenshots can be added to tests while execution)

[wordpressfan]

I'll move this to Done, and we will do the QA on our main feature pull request here: #7197