[AO] Add alerts summary widget to the Alerts page

[mgiota]

📝 Summary

We want to include the alerts summary stats widget, full width one, in the Alerts page using the design described in this figma file.

This may need syncing the filtering done on the alert view and the widget with the urlbar. See example of implementation.

Prerequisite

Before we start the implementation of this ticket, we should first:

• Integrate the shareable alerts table in Observability Alerts page #134887
• Alert Summary Widget - Full Size #145118

Acceptance criteria

• The alerts summary UI components is added to the Alerts page according to the agreed design

[elasticmachine]

Pinging @elastic/actionable-observability (Team: Actionable Observability)

[mgiota]

@katrin-freihofner @liciavale What is the final design for this? Once we agree on the design, I'll update acceptance criteria with the exact components we want to display. Here are a few questions I posted in the Epic ticket

[liciavale]

The latest design can be found here https://www.figma.com/file/EE8RQphgSXcUqpvpPCybFu/Alerts-in-context---Rules-detail-page?node-id=806%3A412229

[emma-raffenne]

Design mentioned above is superseded by the following one: https://www.figma.com/file/EE8RQphgSXcUqpvpPCybFu/Alerts-in-context---Rules-detail-page?node-id=1076%3A501793

[maryam-saeidi]

Duplicated: #148279