feat: add c3-lsp support

lua/lspconfig/server_configurations/c3_lsp.lua

@@ -0,0 +1,21 @@
+local util = require 'lspconfig.util'
+
+return {
+  default_config = {
+    cmd = { 'c3lsp' },
+    root_dir = function(fname)
+      return util.root_pattern 'project.json'(fname) or util.root_pattern '.git'(fname)
+    end,
+    filetypes = { 'c3', 'c3i' },
+  },
+  docs = {
+    description = [[
+https://github.com/pherrymason/c3-lsp
+
+Language Server for c3.
+    ]],
+    default_config = {
+      root_dir = [[root_pattern("project.json", ".git")]],
+    },
+  },
+}