[FEAT]: Add support for managing multiple repository custom properties as a single resource

[mroyme]

Describe the need

We need to add custom property support for repositories to enable ruleset management based on custom properties.

Proposed Implementation

A new resource that manages a collection of custom properties per repository, in contrast to the current implementation which requires one resource per key-value pair (current implementation).

Example Usage:

resource "github_repository" "example" { 
  name        = "example" 
  description = "My awesome codebase" 
}

resource "github_repository_custom_properties" "my_properties" {
  repository = github_repository.example.name 
  
  properties = { 
    gitops-promotion-path      = "main,staging,canary,production"
    gitops-promotion-path-name = "standard"
  }
}

Benefits:

1. Cleaner resource management (one resource per repository instead of one per property)
2. Easier to maintain multiple properties for the same repository
3. Enables efficient ruleset configuration based on repository custom properties

SDK Version

No response

API Version

No response

Relevant log output

Code of Conduct

• I agree to follow this project's Code of Conduct

[github-actions]

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