Feature: right aligned user message variant

[nicolethoen]

Based on the results of the Compass/unified theme dev/design sync on Jan 14 and as a follow up to the design issue patternfly/patternfly-design-kit#907

Implement technical updates to the Chat Message component to support right-aligned user messages and optional metadata. This must be an opt-in change via new props to ensure we do not break existing implementations.

Functional Requirements

1. Alignment Logic

• Variable Alignment: Support a mechanism to switch message alignment between Left (default) and Right.
• User Messages: Support right-alignment within the chat container.
• AI Messages: Should remain full-width/left-aligned.
• Spacing: For right-aligned messages, implement the defined design token for the left margin/padding to maintain the visual offset.

2. Component Variants & Toggles

• Metadata Toggle: Provide props to allow consumers to hide/show:
  • Username and AI Labels
  • Timestamps
  • Avatars (integrating with existing pre-release functionality)
• Default State: Maintain current behavior (Left-aligned, all metadata visible) unless props are explicitly passed.

3. Accessibility (A11y)

• Screen Reader Identity: Ensure that when metadata/avatars are visually hidden, the component still communicates the sender's identity (User vs. AI) to screen readers.
• Logic: Maintain or optimize aria-label logic to announce the sender before the message content.

Use Case Matrix

The implementation must support:

1. Standard: All Left + Metadata Visible
2. Simplified Standard: All Left + Metadata Hidden
3. Threaded: User Right / AI Left + Metadata Visible
4. Simplified Threaded: User Right / AI Left + Metadata Hidden

Acceptance Criteria

• Component supports alignment and visibility toggles without side effects for existing consumers.
• Right-aligned messages respect the design-defined margin tokens.
• Screen readers correctly identify the sender in "Simplified" views.