feat(opencode): added in oauth connection for azure provider through MS Entra ID and az cli

[OpeOginni]

Issue for this PR

Closes #31342
Closes #21658

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This PR adds another login method for the Azure and Azure Cognitive Services providers.

This would be an alternative for teams that don't have access to API keys for the deployed resources.

• Adds instructions and link to Azure docs explaining how to setup proper Roles to use the Resources
• Makes use of the az cli and Bun Spawn to get the access keys to be used, tried the @azure/identity package, but would make Bun and the TUI to crash.
• Updated docs to show that this is now an option.

How did you verify your code works?

Tested locally but logging in fresh to the azure provider using the Oauth method, after completely logging in on the az cli

Screenshots / recordings

Screen.Recording.2026-06-08.at.12.58.05.mov

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR