Add clangd switch source/header mapping

lua/plugins/20-lsp.lua

@@ -13,8 +13,15 @@ return {
             },
             timeout_ms = 1000,
         },
-        -- mappings to be set up on attaching of a language server
+        mappings = {
-        mappings = {},
+            n = {
+                gh = {
+                    require("clangd_extensions.switch_source_header").switch_source_header,
+                    desc = "Switch to matching source or header file",
+                    cond = "textDocument/switchSourceHeader",
+                },
+            },
+        },
         ---@diagnostic disable: missing-fields
         config = {
             clangd = {