Add temporary New badge after setting up KMW

[aaemnnosttv]

Feature Description

This is a follow up to #7376 which added the (static) new badge to KMW but was later removed in #6786. As part of restoring this, we also want to make it temporary.

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Acceptance criteria

• When first setting up the Key Metrics widget, a "New" badge should be shown in the widget area's header, as in the designs
• The badge's display should be temporary and the badge should only be visible for two weeks

Implementation Brief

• When setting the Key_Metrics_Setup_Completed_By value upon successful setup of KMW, set a transient (e.g. googlesitekit_key_metrics_setup_new) to a boolean true, using an expiration of WEEK_IN_SECONDS
• Pass this value to the client unconditionally, along side keyMetricsSetupCompletedBy as keyMetricsSetupCompletedNew
• Use this value on the client to conditionally render the New badge in the widget area as we did before (https://github.com/google/site-kit-wp/pull/7493/files#diff-8684c16fe68eb0a2acb0bd8f481711922ed5b9e2a97b5ac6666718933e84d6fa)

Test Coverage

• Minimal coverage is fine given the time constraints; this should also be easy to verify in QA

QA Brief

• If using an existing test site, do a reset first
• Check that the new badge appears after setting up KMW both ways (tailored metrics + choosing own)
• To simulate the expiration of time that the badge is shown, use a plugin like Transients Manager to clear all transients
• While viewing KMW tiles, the new badge can also be toggled on/off temporarily in the browser (not a replacement for the above)

Changelog entry

• N/A

[kuasha420]

Noting that, upon discussion with @marrrmarrr we decided to make the time two weeks instead of one for now, and will also factor in number of logins since setup in a follow up enhancement to this.

[wpdarren]

QA update: ❌

@kuasha420 I noticed that when I select metrics and save them, the dashboard loads with the widget and the appropriate tiles, but the badge does not load. When I refresh the dashboard, the badge then appears.

Screencast below.

kmw-badge-ui.mp4

I also want to note, more for @aaemnnosttv to get his opinion, but we don't have the new badge on the widget when only the CTA appears, which feels like an odd user experience. I would expect it to appear.

[aaemnnosttv]

@wpdarren the follow-up which addresses your point above has been merged

[aaemnnosttv]

QA + Approval ✅

Tested this a number of ways, and this looks good to go 🚀

• Setting up when choosing Tailored metrics
• Setting up when choosing own metrics
• New badge is shown right after set up is completed and on subsequent page refreshes
• Shows as expected in a view-only context (i.e. set up by another user)
• Disappears after transient expires (set to 2 weeks)

It's worth noting that the New badge does not show on the header of the CTA before the feature is set up, but this is a bit out of scope with the AC as defined and something we can consider as a future enhancement.

Thanks all!