[Log Explorer] Include title and icon in installed packages API

[weltenwort]

📓 Summary

The API that paginates through the installed integrations currently only includes its name, but not the title or icons from the package manifest. Currently the dataset selector shows the name, which is not well formatted. In addition, the <PackageIcon> component it contains has to perform inefficient per-package queries to fetch the icons. We want to improve on both problems by including these data right in the API response.

• 🔗 related to: [Logs+] Implement Data Source APIs #156413
• 🔗 related to: [Logs+] Implement Logs Dataset selector #159907

✔️ Acceptance criteria

• The "installed packages" route at ${EPM_ROOT}/packages/installed includes the following fields:
  • title: string as specified in the integration's package manifest
  • icons: PackageSpecIcon[] as specified in the integration's package manifest
• If possible, the route handler performs at most one more query to fetch all the manifests at once.
• The dataset selector uses the title to display the integration name.
• The dataset selector uses the icons list to pre-populate the <PackageIcon>'s icons list to avoid an API call.

💡 Implementation hints

• We want to use the PackageSpecIcon so the array can be passed to the <PackageIcon> component in the icons prop.
• The package manifests are stored as saved object's of type epm-packages-assets in the data_utf8 field. They can be filtered for using a terms query on the asset_path fields assuming we know the package name and version. If there is a library helper in the fleet plugin to find these asset saved objects we should try to use it.
• The manifest is in yaml format, which needs to be parsed safely and robustly.

[elasticmachine]

Pinging @elastic/infra-monitoring-ui (Team:Infra Monitoring UI)