feat(provider-deepl): omit placeholders plugin option

[Henrixounez]

Changes

Adds an optional boolean omitPlaceholders provider option for the DeepL Provider that handles text inside double curly brackets, that can be used as placeholders or variable text.

Asked by #484 , but I also had the same need with collaborators on Strapi that want to mass translate text with those {{text}} inside.

Explanation

Replicated the process explained in the example provider by Deepl:
https://developers.deepl.com/docs/resources/examples-and-guides/placeholder-tags
https://github.com/DeepLcom/deepl-python/blob/main/examples/mustache/README.md

Steps:

When omitPlaceholders is true

• ⬅️ Before the translation: it creates and fills a temporary placeholderTexts array that contains the text that should be kept, while replacing the text with a simple <m id=xx /> tag to keep the position of the placeholder in the text.

• ➡️ After the translation: it replaces back the tags with the original text thanks to the index saved inside the tag id.