feat(colorscheme): Add Alabaster colorscheme

Author: nullcopy

lua/astrocommunity/colorscheme/alabaster/README.md

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+# aurora
+
+[Tonsky's Alabaster theme](https://github.com/tonsky/sublime-scheme-alabaster) ported to (Neo)Vim.
+
+**Repository:** <https://github.com/p00f/alabaster.nvim>
+
+```vim
+" Vim Script
+colorscheme alabaster
+```

lua/astrocommunity/colorscheme/alabaster/init.lua

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+return { "p00f/alabaster.nvim", lazy = true }