Add React Native EU conference

[JuanPabloDiaz]

fixes #6857

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To get the conferce as fast as possible into confs.tech please consider the following things.

Checklist for your change

• does not delete another conference
• has passed the tests via npm run test
• has the correct order via npm run reorder-confs
• is a developer conference: more than 3-4 people from different companies
• is not a webinar, hackathon, marketing, zoom meeting with one person
• URLs are reachable, as short as possible, do not contain tracking parameters and the website is dedicated for this event
• topic is correct
• conference name is as short as possible and does not include location and date