feat(Message): add default bot message avatar

[kmcfaul]

Closes: #816

Todos -

• pull in new prerelease react versions for Avatar update testing
• update examples: remove avatar src prop from all bot message examples
• update any tests
• pull in new stable versions for Avatar update (6.6)

Open question -

• Do we want to try to set the bot avatar by default like I currently have the logic in Message or would we prefer to instead expand avatar's allowed types to let users pass in the RhUiAiChatbotIcon themselves? Answer - yes to default Avatar, also allowed other types.

[patternfly-build]

Preview: https://chatbot-pr-chatbot-850.surge.sh

A11y report: https://chatbot-pr-chatbot-850-a11y.surge.sh

[thatblindgeye]

Codewise this all looks pretty good to me, just a couple comments beloww. Will re-review once we're able to pull in the latest versions.

Once we do pull in latest versions, could we also update the "User messages" example to show how a consumer can pass in initials+color to a user message? Maybe after the second message in that example, "This is a user message with avatarProps set to add a border." I dont think we need to show all the colors, though.

[mcoker]

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[thatblindgeye]

Now we just wait for official release numbers 😎