Conversation history - separate label prop from aria-label and tooltip content

[thatblindgeye]

Followup to #602 (comment)

Right now the label prop in ChatbotConversationHistoryDropdown applies to both the tooltip and the aria-label of the toggle. Since it'd be more ideal for each of these conversation action toggles to have a unique accessible name, this may not be great in cases where perhaps the accessible name is lengthier, but that causes too large a tooltip.

We should first look into whether having the tooltip be more generic (remaining as "Conversation options"), while the accessible name is fine to be more specific ("conversation options for Some Conversation Name"). This would probably be fine considering visually the context is there for users (the conversation name + the tooltip content), while the accessible name for users of AT would provide the full context they might not be able to get visually. But worth double checking.