feat(dashboard): Show the archived sites when a team has no live sites (backport #7426)

[mergify]

The problem

A team can archive all of its sites. The site list then shows only "No sites".
The user gets no information and no next step.

The archived sites stay in the account. But the status filter removes the
Archived status by default. So the list hides them.

The team in this example has three archived sites and no live site:

The change

The site list changes to the archived view when the team has no live site:

• The page applies the Archived status filter.
• The page shows the archived sites.
• The URL becomes /sites?status=Archived.
• A banner says why the page shows the archived sites.

This is the same team, and the same URL:

A team with no site

A team with no site at all keeps the default list. The page does not change to
the archived view. The user creates the first site from this page.

The status in the URL

The page reads the status filter from the URL. A user can send
/sites?status=Archived as a link.

A status in the URL also stops the automatic change. The user asked for that
status.

Vue keeps this page when only the query changes. The back button is an example.
So the page watches the status in the URL, and applies the new status.

The check for live sites

The page uses the result of the count request that it makes already. It does not
make a new request. That request has no shared cache. So its result is always
the live sites of the current team.

The page makes the check one time on the first load. It makes the check again
after the user archives a site. It does not make the check for a different
filter. An empty result for a region or a tag does not move the user.

Tests

I used a local bench and the dashboard development server. I made two demo
teams: one team with three archived sites, and one team with no site.

Test	Result
The team has live sites	/sites, no banner, the live sites in the list
The team has archived sites only	/sites?status=Archived, the banner, the archived sites in the list
The team has no site at all	/sites, no banner, the default list and the New Site button
A link to /sites?status=Archived, and the team has live sites	The Archived filter stays, and there is no banner
The sidebar Sites link, from /sites?status=Archived	The URL and the filter go back to the live statuses
The user drops the last live site from the list	The page changes to the archived view, with no reload

---

This is an automatic backport of pull request #7426 done by [Mergify](https://mergify.com).

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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