Add explicit support for 'mini.nvim'

[echasnovski]

This PR adds explicit support for 'echasnovski/mini.nvim'. Some notes:

• Not all available groups are defined because the rest seem to look good with default links/definitions.
• Colors for 'mini.indentscope', 'mini.jump2d', and 'mini.statusline' are using 'indent-blankline.nvim', 'hop.nvim', and 'lualine.nvim' for reference.
• Colors for 'mini.icons' are taken as the closest in hue to the hue in name.
• Groups for 'mini.test' are present just in case, because their default colors are inferred from vim.g.terminal_color_{1,2} which is not really clean.
• Others mostly follow how I prefer those groups to be colored. So a matter of preference how they should be colored, just not as from default links (for better usability).

[Shatur]

Thank you!