Change the constructor to accept role and a single content item instead
of raw AvanteLLMMessage instance. This will help when we will start
changing message.content from being a string or a list of tables to just
a string or a single table.
It is unwieldy to handle fields in opt table one by one. Luckily there
is vim.bl_extend("force", ...) that can help us here.
Also move annotation for opts from parameter to a separate class to make
it easier to work with.
The utils module has grown too big and contains unrelated functionality.
Start moving code related to managing history messages comprising chat
history into lua/avante/history module to keep the code more manageable.
