Move lsp config to local file structure

.config/nvim/lsp/starlark_rust.lua

@@ -0,0 +1,16 @@
+---@brief
+---
+--- https://github.com/facebookexperimental/starlark-rust/
+--- The LSP part of `starlark-rust` is not currently documented,
+--- but the implementation works well for linting.
+--- This gives valuable warnings for potential issues in the code,
+--- but does not support refactorings.
+---
+--- It can be installed with cargo: https://crates.io/crates/starlark
+
+---@type vim.lsp.Config
+return {
+  cmd = { 'starlark', '--lsp' },
+  filetypes = { 'star', 'bzl', 'BUILD.bazel' },
+  root_markers = { '.git' },
+}