🔒 Change Linear authentication to OAuth

[mlamina]

This PR changes the Linear authentication method from API key to OAuth, enhancing security and user experience.

Changes

• Database Migrations

  • Rename api_key field to access_token in LinearIntegration model.

• Models

  • Update LinearIntegration model to use access_token instead of api_key.

• Templates

  • Update integrations.html to reflect changes in Linear integration.
  • Add detailed descriptions for Slack and Linear integrations.

• URLs

  • Add new URL pattern for Linear integration callback.

• Views

  • Add add_linear_integration view to handle OAuth callback for Linear.
  • Update add_slack_integration view to include redirect URI.

• Settings

  • Add LINEAR_CLIENT_ID and LINEAR_CLIENT_SECRET to settings.

• Version

  • Bump version to 1.4.2.

• Tests

  • Update end-to-end tests to reflect changes in Linear integration.

• Integration Tools

  • Update Linear integration tools to use OAuth access token.
  • Add support for creating issues in Linear by team name.

• Miscellaneous

  • Remove unused fork_issue import in pr_pilot_agent.py.

[pr-pilot-ai[bot]]

The unit tests have failed. Here are the files that caused the failures:

• e2e_test.py
• prpilot/settings.py

Please review the changes and address the issues accordingly.