feat(ENG-11506): initiate OAuth flow with integration id

[adefreitas]

Summary by cubic

Switch OAuth initiation to use integration_id in the URL path and remove the provider_version param, so the new hub sends the integration ID during account creation. Aligns with ENG-11506 and ensures the OAuth flow routes to the correct integration.

^{Written for commit 1adc381. Summary will update automatically on new commits.}

[Copilot]

Pull request overview

This PR updates the OAuth flow to use integration_id instead of provider as the URL parameter, and removes the provider_version query parameter from the OAuth redirect URL.

• Changed OAuth endpoint from provider-based to integration_id-based routing
• Removed provider_version query parameter from OAuth URL construction

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[joeStackOne]

LGTM