refactor: revamp add OpenAPI route

[kigawas]

Description

This PR fixes

• OpenAPI routes should be added after _check_port
• logger.info("Docs hosted at http://%s:%s/docs", host, port) was not correct. It just ignored ROBYN_HOST and ROBYN_PORT

Summary

• Extract adding OpenAPI routes
• Add auth_required argument for future implementation
• Adjust the order to output the correct log

PR Checklist

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• The PR contains a descriptive title
• The PR contains a descriptive summary of the changes
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• You have added relevant documentation
• You have added relevant tests. We prefer integration tests wherever possible

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[sansyrox]

Hey @kigawas 👋

Thanks for the PR 😄 One follow up - how did you find this issue?

[kigawas]

@sansyrox
I was setting ROBYN_PORT directly and the log's port was different

[sansyrox]

Looks good to me 😄