fix sftp for custom private networks

[eliferrous]

Change Summary

What and Why:
this is referenced in our docs but wasn't included in the changes to add custom network support to flyctl in #3447

How:
copies changes to ssh/console.go to allow the agent to access the app's network

Related to:
https://github.com/superfly/flyctl/pull/3447/files

Documentation

• Fresh Produce
• In superfly/docs, or asked for help from docs team
• n/a

[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ *errors.errorString: failed probing "personal": context deadline exceeded github.com/superfly/flyctl/internal/sentry in C... View Issue
• ‼️ *errors.withStack: error saving config file: open C:\Users\cuthb.fly\config.yml: Access is denied. github.com/superfly/flyctl/internal/wireguard i... View Issue

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