feat(nvim): add nvim-lint with rubocop

Basic setup from [^1]. Basic bundle integration found in [^3].

Open issues:
- Linting fails when rubocop is not available in the bundle.
  One can provide a function for the linter[^2] and should be able to
  use either the bundled rubocop, or a global rubocop as fallback.
- When rubocop itself fails (with error code 2), like when it sees an
  unrecognized cop in .rubocop.yml, this is unnoticed during editing.
- Make rubocop run on BufReadPost, InsertLeave, and TextChanged events.
  This is mentioned in mfussenegger/nvim-lint#336

[^1]: dietrichm/dotfiles#138
[^2]: mfussenegger/nvim-lint#18
[^3]: https://github.com/pfeiferj/dotfiles/blob/9fe44801e52590610d2090f2c03df6fbb31b6f57/dot_config/nvim/lua/plugins/lint.lua

.config/nvim/lazy-lock.json

@@ -14,6 +14,7 @@
   "mason.nvim": { "branch": "main", "commit": "d66c60e17dd6fd8165194b1d14d21f7eb2c1697a" },
   "neodev.nvim": { "branch": "main", "commit": "e683583f8ba2f9dbbc4539889cbbdbfc5afb5fb2" },
   "nvim-cmp": { "branch": "main", "commit": "5dce1b778b85c717f6614e3f4da45e9f19f54435" },
+  "nvim-lint": { "branch": "master", "commit": "67f74e630a84ecfa73a82783c487bdedd8cecdc3" },
   "nvim-lspconfig": { "branch": "master", "commit": "ede4114e1fd41acb121c70a27e1b026ac68c42d6" },
   "nvim-surround": { "branch": "main", "commit": "0d6882635817a2677749a330127d12ac30a4f3c8" },
   "nvim-treesitter": { "branch": "master", "commit": "b5873bacb4ce44e0aac313abb28bb72e67fc9a53" },
@@ -28,4 +29,4 @@
   "vim-sleuth": { "branch": "master", "commit": "1cc4557420f215d02c4d2645a748a816c220e99b" },
   "which-key.nvim": { "branch": "main", "commit": "7ccf476ebe0445a741b64e36c78a682c1c6118b7" },
   "yadm-git.vim": { "branch": "master", "commit": "dbf067f99ccfc000659dfef846230148ee22e388" }
-}
+}

.config/nvim/lua/plugins/nvim-lint.lua

@@ -0,0 +1,18 @@
+return {
+  "mfussenegger/nvim-lint",
+  config = function()
+    local rubocop = require('lint').linters.rubocop
+    rubocop.cmd = 'bundle'
+    rubocop.args = { 'exec', 'rubocop', '--format', 'json', '--force-exclusion' }
+    -- rubocop.stdin = true
+    require('lint').linters_by_ft = {
+      ruby = {
+        "rubocop"
+      }
+    }
+    vim.api.nvim_create_autocmd(
+      { "BufWritePost" },
+      { callback = function() require("lint").try_lint() end, }
+    )
+  end
+}