Allow table as additional args in live grep and grep string

[gepbird]

Description

Currently you need to wrap additional arguments for live grep (and grep string) in a function that returns a table. This PR allows using just a table too.

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

Minimal config:

require 'telescope'.setup {
  defaults = {
    vimgrep_arguments = { 'rg', '--column' }
  }
}

Have hidden and non-hidden files in the current working directory. Open live grep with the options specified in the following tests.
Search for a hidden file to test if telescope used the specified options for grepping.

• Using a function for additional args still works

require 'telescope.builtin'.live_grep {
  additional_args = function(opts) return { '--hidden' } end
}

• Using a table for additional args now works

require 'telescope.builtin'.live_grep {
  additional_args = { '--hidden' }
}

Test are identical for grep_string.

Configuration:

• Neovim version (nvim --version): v0.8.0-dev-788-g0fdf59ac9
• Operating system and version: arch linux 5.19.1-arch2-1

Checklist:

• My code follows the style guidelines of this project (stylua)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (lua annotations)

[Conni2461]

sorry for the long wait. I rebased it and generated vimdocs.

Thanks :)