[Fleet] Add a new "integrations" tab that lists all integration policies

[kpollich]

User story

As a Fleet user, I want to access a high-level summary of all my integration instances across my fleet of agents, so I can perform bulk actions, upgrade outdated integrations, and easily search and manage my integrations.

Acceptance criteria

Integrations tab

• A new "Integrations" tab exists as the left-most tab in Fleet's tab-based navigation

Integrations table

• The Integrations tab displays a paginated table listing all integration policies
• The table's columns include
  • Instance name - Displays the name of the integration policy
  • Policy - Shows the associated agent policy name. Includes multiple policies through a pop-out on hover + policy count, as we display elsewhere
  • Integration type - Title of the associated integration
  • Version - Current version of the integration on this policy. Displays an "upgrade available" badge for outdated versions
  • Actions - Allows access to the same actions that are available on the integration policies table within the integrations UI today

Bulk upgrade action

• A new “Upgrade All” button is available in the upper-right, enabling users to upgrade all integrations to the latest version at once.
  • Selecting “Upgrade All” triggers a confirmation modal to confirm the bulk operation.
  • Upon initiating the bulk upgrade, a toast message displays the pending status.
  • Once completed, another toast message indicates the success or failure of the operation.

Mockups

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)