Feature: enhance MessageBar layout for chat modes

[nicolethoen]

Follow up to patternfly/patternfly-design-kit#901

implement updated MessageBar pattern per the Genie user input concepts: https://www.figma.com/design/lJ5s1z11E4Q2Bp6kD3TE0W/Red-Hat-Project-Genie?node-id=353-5202&p=f&m=dev

• plus sign button/toggle to the left of the input which opens a menu
• selected 'mode' appears in a dismissible label below the input - inline with the send and microphone buttons. input moves up and takes up 100% width of message bar

Figma from PF design: https://www.figma.com/design/MSr6kVEOuAxmPOkjg7x8PO/branch/ha4o1q3giw8STVZAgYGHwG/PatternFly-6--Patterns---Extensions?m=auto&node-id=5190-4959&t=mxvl12unSfVHNnn4-1

[thatblindgeye]

A similar ask/implementation was brought up in the 12/4/2025 chatbot sync by Lightspeed, see their figma file (the "Chatbot UI Update - Message Bar" section)

[thatblindgeye]

This shoud also include a Model Selector in a multiline layout, below the input and to the left of the send button, or rather just creating a layout for below the message input for whatever actions a consumer wants to add