[Logs Explorer] Last activity indicator on DataSourceSelector datasets

[tonyghiani]

📓 Summary

🛑 Blocked by #177696

To help the user know which datasets are mostly active and prevent the "select and empty dataset" scenario, we want to display when the last activity occurred at the integration and dataset level.

🎨 Design

The final design is still pending and there is a proposal linked on this Figma page that is going to be tested before being ready for implementation.

✔️ Acceptance Criteria

• Should display a last activity indicator next to each dataset.
• Should display a last activity indicator next to each integration, which results in the latest activity from any of the integration's datasets.
• Should allow sorting by last activity upon clicking on the column header.
• Should format the last activity indicator in a relative format (1 minute ago, 2 hours ago, ...)

💡 Implementation hints

• We can update the currently used installed list packages API to also return this detail for each dataset.
• It might impact the performance of the API due to collecting this detail from a different source, so please be concerned about measuring performance after the change ⚡

❓ Open questions

• How often do we want to refresh the last activity value in the background? Is this something desirable?
• Is it desirable for the user to have a manual refresh action item to update the last activity indicator?

[elasticmachine]

Pinging @elastic/obs-ux-logs-team (Team:obs-ux-logs)