Allow for config file path to be passed to rubocop

[mtraina8]

#262 (comment) for context

Briefly, I'd like to be able to run erblint in our CI that has restrictions on writing to its current directory. Since Rubocop lacks an api to read in a config that is not a file, we must give it a path. This PR adds support for passing a config path to rubocop instead of the gem writing to the current directory and passing that file to rubocop.

Thanks to @etiennebarrie for your proposal

Usage

--- # .erb-lint.yml
EnableDefaultLinters: true
linters:
  Rubocop:
    enabled: true
    config_file_path: .rubocop.erb-lint.yml

--- # .rubocop.erb-lint.yml
inherit_from:
  - .rubocop.yml
  # more here

[rafaelfranca]

Can you please document how to use this new config?