modules/lsp: move server module to dedicated file

modules/lsp/server.nix

@@ -0,0 +1,50 @@
+{ lib, ... }:
+let
+  inherit (lib) types;
+in
+{
+  options = {
+    enable = lib.mkEnableOption "the language server";
+
+    activate = lib.mkOption {
+      type = types.bool;
+      description = ''
+        Whether to call `vim.lsp.enable()` for this server.
+      '';
+      default = true;
+      example = false;
+    };
+
+    package = lib.mkOption {
+      type = with types; nullOr package;
+      default = null;
+      description = ''
+        Package to use for this language server.
+
+        Alternatively, the language server should be available on your `$PATH`.
+      '';
+    };
+
+    config = lib.mkOption {
+      type = with types; attrsOf anything;
+      description = ''
+        Configurations for each language server.
+      '';
+      default = { };
+      example = {
+        cmd = [
+          "clangd"
+          "--background-index"
+        ];
+        root_markers = [
+          "compile_commands.json"
+          "compile_flags.txt"
+        ];
+        filetypes = [
+          "c"
+          "cpp"
+        ];
+      };
+    };
+  };
+}