Draft: Add topics support to repository module

Summary

This MR adds GitLab topics support to the repository module.

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Changes

• Repository Module: Added topics attribute to gitlab_project resource
• Variables: Added additional_topics and enable_default_topics variables
• Default Topic: Automatically assigns flight-deck-managed topic to identify Flight Deck managed repositories
• Documentation: Updated module README with usage examples and configuration options
• FAQ: Added questions about identifying and customizing topics for Flight Deck managed repositories

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Usage

# Default - adds "flight-deck-managed" topic
inputs = {
  name = "my-repo"
}

# Add custom topics
inputs = {
  name = "my-repo"
  additional_topics = ["cli", "tool"]
}

# Disable defaults
inputs = {
  name = "my-repo"
  enable_default_topics = false
}