BED-4624 fix: missing error handling during sso login

[mistahj67]

Description

• Moved RedirectToLogin fn to api due to cyclic import requirement
• Fixed redirect to actually redirect to login uri instead of root ui
• Added additional error handling for session creation

Motivation and Context

This PR addresses: BED-4624

Why is this change required? What problem does it solve?
Support for displaying errors in the UI that occur during sso login

How Has This Been Tested?

Locally

Types of changes

• Chore (a change that does not modify the application functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have met the contributing prerequisites
  • Assigned myself to this PR
  • Added the appropriate labels
  • Associated an issue: Issues and Pull Requests README #672
  • Read the Contributing guide: https://github.com/SpecterOps/BloodHound/wiki/Contributing
• I have ensured that related documentation is up-to-date
  • Open API docs
  • Code comments (GoDocs / JSDocs)
• I have followed proper test practices
  • Added/updated tests to cover my changes
  • All new and existing tests passed

[ALCooper12]

LGTM! Changes make sense