[Localization] Guidelines for large paragraphs and markdown

[Bamieh]

Summary

Our i18n guide does not specify how developers should handle internationalizing large paragraphs of text and markdown.

Concerns

Without specific guidelines for devs translators might find them selves in a mix of confusing messages to be translated leading to a few back and forth conversations to understand the context of these messages.

We don't have anything specific for markdown but ideally the i18n messages should not include the actual markdown identifiers (#, *, _, etc)

End goals

Additional documentation is needed in the kbn-i18n/GUIDELINE:

1. Add a section for handling markdown text
2. Add a section for handling large paragraphs of text

We handle large text and new lines. we just need to update the guidelines to note that.

Potential solutions

Markdown

After a few discussions with our translators; we need a way to identify markdown messages separately for their parser. One solution is to postfix markdown ids with .markdown for messages containing MD.

we have a list of supported markdown agreed with the translators which we should update the GUIDELINES to list them.

Large paragraphs

We have guidelines about splitting sentences here; https://github.com/elastic/kibana/blob/master/packages/kbn-i18n/GUIDELINE.md#splitting

We can split paragraphs into a few i18n chunks whenever makes sense. we just have to be mindful for the i18n messages to make sense for the translators.

[elasticmachine]

Pinging @elastic/kibana-localization (Team:Localization)

[Bamieh]

Example PR where this is needed in lens: https://github.com/elastic/kibana/pull/99297/files#diff-db1b18680c92626a2753436ff80ee8efb1de50c389599bff0f6208b3a42f5562

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)