BED-5066: Better error messaging when creating SSO providers

[wes-mil]

Description

Add better API response when failing to create new SSO provider and change corresponding UI elements.

Motivation and Context

This PR addresses: BED-5066

Previously, a name conflict when creating a new SSO provider would provide an nondescript error which didn't provide the user with any actionable information.

How Has This Been Tested?

Attempting to create a new SSO provider with a duplicate name now returns a 409 status code with a descriptive error message. When this error is hit on the UI it indicates to the user what specifically went wrong.

Screenshots (optional):

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• I have met the contributing prerequisites
  • Assigned myself to this PR
  • Added the appropriate labels
  • 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