feat: Add Knowledge Graph enable and disable commands

Summary

Introduce a ChatOps command to enable or disable the Knowledge Graph for a root namespace to seed the service during the initial stages of the launch.

Later, we will have a background worker that will be fully automatic, but we probably can't do that right away. I'd expect that we'd first enable it for some namespaces at first, and possibly some customers who really want to participate, and switch to the worker when we're ready.

Tests

Test Data

id	name	parent_id
35	Acme Corp
95	Acme Sub	35

Test Script

GITLAB_TOKEN='xxxx' bundle exec ruby -I lib -e "
require 'chatops'

client = Chatops::Gitlab::Client.new(
  token: ENV['GITLAB_TOKEN'],
  host: 'localhost:3000'
)

puts '=== Enable root namespace (Acme Corp, id=35) ==='
begin
  result = client.knowledge_graph_enable_namespace(35)
  puts 'SUCCESS: ' + result.inspect
rescue => e
  puts 'FAILED: ' + e.class.name + ': ' + e.message
end

puts
puts '=== Enable subgroup (Acme Sub, id=95) - should fail ==='
begin
  result = client.knowledge_graph_enable_namespace(95)
  puts 'SUCCESS: ' + result.inspect
rescue => e
  puts 'FAILED: ' + e.class.name + ': ' + e.message
end

puts
puts '=== Disable root namespace (Acme Corp, id=35) ==='
begin
  client.knowledge_graph_disable_namespace(35)
  puts 'SUCCESS: Disabled'
rescue => e
  puts 'FAILED: ' + e.class.name + ': ' + e.message
end
"

Test Output

=== Enable root namespace (Acme Corp, id=35) ===
SUCCESS: #<Gitlab::ObjectifiedHash:5560 {hash: {"id"=>4, "root_namespace_id"=>35, "created_at"=>"2025-12-11T16:29:22.280Z"}}

=== Enable subgroup (Acme Sub, id=95) - should fail ===
FAILED: Gitlab::Error::BadRequest: Server responded with code 400, message: Namespace must be a root namespace. Request URI: http://localhost:3000/api/v4/admin/knowledge_graph/namespaces/95

=== Disable root namespace (Acme Corp, id=35) ===
SUCCESS: Disabled

Issue

Resolves gitlab-org/gitlab#582318