Fix LSP and update plugins

- Structure LSP configuration code
- Since `lsp-zero` is deprecated, instead use `nvim-lspconfig`
- Use `nvim_lsp_signature_help` instead of `lsp_signature`

nvim/lua/lsp/git.lua

@@ -0,0 +1,7 @@
+require('vgit').setup({
+    settings = {
+        signs = {
+            priority = 0,
+        },
+    }
+})