Add configuration for OpenAI prompt

[michaelbaudino]

The default prompt now includes instructions to never translate HTML tags (e.g. <strong>) nor Ruby I18n variables (e.g. %{count}).

This PR also makes the system prompt passed to OpenAI configurable directly from i18n-tasks.yml.

Incidentally, it also fixes a Rubocop offense.

This is a followup of #532.

[glebm]

The settings in this file are formatted so that uncommenting turns them into valid options.
Please move the comment above the line and add the appropriate multiline string sigil.

[michaelbaudino]

I just changed it as I think you requested 👍

I tried to make it consistent with what was done for Deepl configuration, for both mandatory configuration lines, optional (commented) configuration lines and plain old comments (with plain old English).

I used a folded style indicator (>) with a "stripping" block chomping indicator (-) to explicitly indicate the multiline field and how it will be processed (resulting in a >- marker): it seems to me it was the more logical processing method to apply, but I'm happy to change it if you prefer another one.

I hope that's what you expected.

---

On a side note, though, I'm pretty sure the previous implementation was still valid YAML when uncommented (despite the end-of-line comment and the lack of explicit multiline indicator 🤷):

YAML.safe_load(<<~YAML)
  openai_system_prompt: # may contain `%{from}` and `%{to}`, which will be replaced by source and target locale codes, respectively (using `Kernel.format`)
    You are a professional translator that translates content from the %{from} locale
    to the %{to} locale in an i18n locale array.
  
    The array has a structured format and contains multiple strings. Your task is to translate
    each of these strings and create a new array with the translated strings.
  
    HTML markups (enclosed in < and > characters) must not be changed under any circumstance.
    Variables (starting with %%{ and ending with }) must not be changed under any circumstance.
  
    Keep in mind the context of all the strings for a more accurate translation.
YAML
# => {"openai_system_prompt"=>
#      "You are a professional translator that translates content from the %{from} locale to the %{to} locale in an i18n locale array.\nThe array has a structured format and contains multiple strings. Your task is to translate each of these strings and create a new array with the translated strings.\nHTML markups (enclosed in < and > characters) must not be changed under any circumstance. Variables (starting with %%{ and ending with }) must not be changed under any circumstance.\nKeep in mind the context of all the strings for a more accurate translation."}

YAML is such a pain

[glebm]

Indeed, YAML is gnarly. Thanks!

[michaelbaudino]

Thanks to you for all the work on this gem 🙏 💜