feat: adding new resource detector for railway.com

[kartikgola]

• I have read and followed the Contributing docs, especially the "First-time contributing?" section.
• This PR has content that I did not fully write myself.
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This is a resource detector for the popular PaaS platform Railway.com.
This resource detector captures the ENV vars provided by Railway and converts them to OTel Semantic Convention resource attributes.

I have also created a test Go app deployed on railway using this public repo : https://github.com/kartikgola/railway-sample-go-app. The deployed app can be accessed at https://amused-purpose-production-4ac8.up.railway.app and it prints the resource attributes detected by the detector.

Footnotes

1. Yes, I can answer maintainer questions about the content of this PR, without using AI. ↩

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