Change background color on response action buttons

[rebeccaalpert]

This has to do with https://www.patternfly.org/patternfly-ai/chatbot/messages#message-actions-clicked-state.

Design would like to make some visual updates to the focus state/clicked state on response actions to resolve some confusing color issues on select/hover/tab. We just want to change the focus state highlight color to be var(--pf-v6-c-button--hover--BackgroundColor) and leave the clicked state the existing white.