enable `update_in_insert` only for certain extensions

Question

I have several LSP servers I use in neovim with nvim-lspconfig. Some are fast, and most are slow. I can make the diagnostics update while in insert mode by doing something like

    vim.lsp.handlers['textDocument/publishDiagnostics'] = vim.lsp.with(
      vim.lsp.diagnostic.on_publish_diagnostics, {
        update_in_insert = true,
      }
    )

However, it's distracting and slow for my slow LSP servers. I'd like a way to enable update_in_insert for only my fast plugins.

Question 1: Is this possible today in Neovim/nvim-lspconfig?

Question 2: If not, I'd like to contribute this to the Neovim project. Where would I start when it comes to contributing this patch?