Feat: Customizable colors for seperators/ transparent outer seperators

[TheRealGLH]

Requested feature

Either for separators to be able to have their own colours set in the config, or for the tail end ones (ie. the left separator for A, and the right separator for Z) to respect the background set for NeoVim.
Although the latter seems like the one that'd be easiest for users to deal with, I don't know how feasible that would be in regards to the highlight system NeoVim uses.

Motivation

In the case of my config:

return {
    "nvim-lualine/lualine.nvim",
    config = function()
        require("lualine").setup({
            options = {
                theme = 'dracula',
                disabled_filetypes = {
                    --'neo-tree',
                    --'toggleterm',
                    'alpha',
                },
                ignore_focus = {
                    'neo-tree',
                    'toggleterm',
                    'netrw',
                    'TelescopePrompt',
                    'mason',
                    'lazy',
                },
                globalstatus = true,
                always_show_tabline = false
            },
            sections = {
                lualine_a = { { 'mode', separator = { left = '' }, right_padding = 2 } },
                lualine_c = { --'filename',
                    function()
                        return require("nvim-treesitter").statusline({
                            indicator_size = 90,
                            type_patterns = { "class", "function", "method" },
                            separator = "  ",
                        })
                    end
                },
                lualine_x = {},
                lualine_y = {},
                lualine_z = {
                    { 'location', separator = { right = '' }, left_padding = 2 },
                },
            }
        })
    end
}

The outer separators for sections A and Z still have a visible background that's the same color as the text for the highlight itself, which makes it looks like it's not quite there yet:

In this case it's not extremely noticeable, because the glyph itself takes up most of the character space, but for Powerline symbols like \ue0ba it's quite jarring, especially if your terminal background is translucent: