support grisp_tools 2

[tonnenpinguin]

Building on top of @LostKobrakai and @ziopio 's work this is now fully functional.

I dropped all distillery related code, changed the logic that calculates the apps to use the source directory. This is required because those directories are used to assemble the overlays and the build output directories don't include those files.

I also updated the readme, as the paths mentioned don't work, since grisp_tools is very picky about the paths being used.

And finally I also updated the grisp.ini.mustache erl arguments to get things working with Elixir 1.16 & OTP 26 (the flags required for iex changed) and to deal with the fact that mix releases rely on a boot_var RELEASE_LIB to be set

[ziopio]

First of all thanks very much for this contribution!
I think we can just set the bar to use elixir 1.16 and OTP 26 and update the references to point to such versions.
I also needed to add xmerl to the mix_grisp applications sections, otherwise mix does not load xmerl and grisp_tools fails.

  def application() do
    [
      extra_applications: [:logger, :xmerl]
    ]
  end

Then I will squash and merge.

[tonnenpinguin]

Thanks for the review @ziopio
I addressed all your comments 🙂