BED-4291 refactor: cleanup orphaned SAML logic and persist root uri versions to db

[mistahj67]

Description

• Cleaned up the old orphaned SAML logic
• Cleaned up saml_provider_id from users and reliance on it in business logic
• Cleaned up multi-instantiation of resources during routing bootstrapping
• Introduce root_uri_version to saml_providers in DB as a solution for maintaining backwards compatibility with existing SAML providers
• Add /metadata endpoint to new SSO structure

Motivation and Context

This PR addresses: BED-4291

Why is this change required? What problem does it solve?

A lot of the old SAML logic needed to be cleaned up once generalized SSO support was added. Additionally, this enables a way for existing SAML providers to exist while new SAML providers can rely on the new SSO auth flow

How Has This Been Tested?

Unit tests + locally

Types of changes

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

Checklist:

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