[Fleet] Support expanding YML fields in integration policy editor

[zez3]

User Story

As a user configuring integrations, I want to expand the YML field editor to full screen, so that I can easily view and edit the full content without relying on scrolling.

Context

The current YML field editor in the integration policy editor is a small, scrollable text box. For large configurations, it becomes difficult to navigate the content by scrolling left/right or up/down. Allowing users to expand the editor to full screen will provide a better user experience, ensuring they can view and edit the entire configuration comfortably.

There are examples of this kind of experience in the EuiCodeBlock component docs, e.g.

Acceptance Criteria

• Add an "Expand" button to the YML field editor, allowing users to open it in a full-screen modal.
• Include a "Collapse" or "Close" button in the expanded view to return to the inline editor.
• Retain all existing functionality for saving or canceling changes to the YML field.

[zez3]

@elastic/fleet (Team:Fleet)

[kpollich]

Thanks for the report, this looks good. I'm going to hijack this with a new title + description and get this scheduled.