How to change indent size to 2 spaces?

[gepbird]

I know that creating a rustfmt.toml file in the project root containing tab_spaces = 2 works, but is there a way to make it the default?
By making it the default I'm thinking of some neovim config, for example this is how I do that for python:

require 'null-ls'.setup {
  sources = {
    null_ls.builtins.formatting.autopep8.with {
      extra_args = {
        '--indent-size=2',
      },
    },
  },
}