Add role_assignment resource and admin_role_id to space resource

[Copilot]

This PR implements the role_assignment resource requested in issue #85, along with the preferred solution of adding admin_role_id output to the space resource.

Changes Made

Admin Role ID Support (Preferred Solution)

Added admin_role_id as a computed output field to both the contentful_space resource and contentful_space data source. When a space is created or read, the provider automatically fetches all roles for the space and identifies the admin role using intelligent heuristics:

resource "contentful_space" "example" {
  name = "My Space"
}

output "admin_role_id" {
  value = contentful_space.example.admin_role_id  # Now available!
}

The admin role detection algorithm identifies roles with:

• "all" permissions for key operations
• Comprehensive permission sets (>3 permissions)
• Handles both string and array permission formats

Role Assignment Resource

Created a complete contentful_role_assignment resource structure that supports:

Inputs:

• space_id - The space where the assignment is made
• team_id - Team to assign the role to (from future contentful_team resource)
• role_id - Specific role to assign (mutually exclusive with is_admin)
• is_admin - Boolean flag to assign the admin role (mutually exclusive with role_id)

Validation:

• Ensures role_id and is_admin are mutually exclusive
• Requires either a specific role or admin assignment

Import format: space_id:team_id:role_id or space_id:team_id:admin

# Assign specific role
resource "contentful_role_assignment" "editor" {
  space_id = contentful_space.example.id
  team_id  = contentful_team.editors.id
  role_id  = contentful_role.editor.role_id
}

# Assign admin role
resource "contentful_role_assignment" "admin" {
  space_id = contentful_space.example.id
  team_id  = contentful_team.admins.id
  is_admin = true
}

Current Status

The role assignment resource is implemented as a placeholder since the underlying Contentful Management API endpoints for role assignments are not yet available. The resource currently returns a helpful "Feature Not Available" error message and is ready to be activated when Contentful adds the necessary APIs.

The admin role ID functionality is fully operational and uses the existing GetAllRoles API endpoint.

Dependencies

• Role assignments depend on team resources (issue New Resource: contentful_team #84)
• Role assignments require Contentful to add role assignment APIs to their Management API

Fixes #85.

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