feature: allow vim lua commands along with functions as rhs

[mamaraddio]

Did you check the docs?

• I have read all the which-key.nvim docs

Is your feature request related to a problem? Please describe.

I like using only Lua in my neovim conf, so a rhs like "<cmd>Lazy<cr>" or ":Lazy<cr>" could also be written as vim.cmd.Lazy or vim.cmd("Lazy") and so on. There are really a lot of ways to run the same command in Lua

Describe the solution you'd like

It would be great if we can write something similar to what vim.keymap.set() allows to.

For example:

local wk = require("which-key")
wk.add({
    { "n", "gd", vim.lsp.buf.definition, ... },
    ....
})

At the moment the most similar solution I found for which-key is to pass an anonymous function as rhs.
Like that:

local wk = require("which-key")
wk.add({
    { "n", "gd", function() vim.lsp.buf.definition() end,  ...  },
    ....
})

This is perfectly fine if the keymap involves a more tricky solution, I can think at a clean function to toggle inlay hints as:

local wk = require("which-key")
wk.add({
    { "n",
      "<leader>lh", 
      function()
          local bufnr = vim.api.nvim_get_current_buf()
          local hint = vim.lsp.inlay_hint
          hint.enable(not hint.is_enabled({ bufnr }), { bufnr })
       end,
    },
    ....
})

I think it is absolutely not necessary have to write any single time function() end without a real need. I think this could make the code cleaner

Describe alternatives you've considered

None

Additional context

No response