feat: support for passing highlight group names

[nenikitov]

Hello,

I added an option to pass highlight group names to components for better color scheme support. For example:

{
    text = function(buffer)
        return buffer.unique_prefix
    end,
    highlight = 'Comment'
},

Similarly to other options, highlight accepts both string with the highlight group name and function(buffer) -> string.

When highlight is passed, fg, bg, and style parameters are ignored.

[willothy]

Lgtm! Thanks for the contribution :)