[docs] Guide how to add SAML to a deployment

[Kushmaro]

trafficstars

Description

Added a guide that should render on the terraform registry docs site, to explain how customers should approach spinning up an Elastic Cloud deployment with a preconfigured SAML provider.

Motivation and Context

This is a common customer use case, that is a bit tricky to achieve.

How Has This Been Tested?

Rendering wasn't tested, but outcome of article was.

Types of Changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Refactoring (improves code quality but has no user-facing effect)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Documentation

[cla-checker-service[bot]]

💚 CLA has been signed

[Kushmaro]

Since the jenkins failure doens't really seem to relate to this change (which is doc only), I'm merging despite the failure.

deployment_basic_test.go:44: Step 3/4 error: Error running apply: exit status 1
14:46:51          
14:46:51          Error: Provider produced inconsistent result after apply
14:46:51          
14:46:51          When applying changes to ec_deployment_traffic_filter.second, provider
14:46:51          "provider[\"registry.terraform.io/hashicorp/ec\"]" produced an unexpected new
14:46:51          value: Root resource was present, but now absent.
14:46:51          
14:46:51          This is a bug in the provider, which should be reported in the provider's own
14:46:51          issue tracker.