Add pg to active_context

What does this MR do and why?

This MR adds PostgreSQL support to the gitlab-active-context gem by introducing a modular database adapter system. Specifically, it:

1. Implements a base adapter architecture with three main concerns:

   • Adapter - Base interface for database adapters
   • Client - Database client abstraction
   • QueryResult - Enumerable result set wrapper

2. Adds the first concrete implementation for PostgreSQL, including:

   • Postgresql::Adapter - Main adapter implementation
   • Postgresql::Client - PostgreSQL-specific client with PG gem integration
   • Postgresql::QueryResult - Result set implementation for PostgreSQL queries

3. Updates the configuration system to properly handle database adapters and adds the pg gem dependency

Why is this needed?

This change provides a foundation for database integrations in the active-context system, starting with PostgreSQL support. The modular adapter design allows for:

• Clean separation of database-specific code
• Consistent interface across different database implementations
• Easy addition of new database adapters in the future

Technical Details

Usage Example

docker run --rm -e "POSTGRES_PASSWORD=password" -p5432:5432 postgres

ActiveContext.configure do |config|
  config.enabled = true
  config.databases = {
    pg1: {
      adapter: 'ActiveContext::Databases::Postgresql::Adapter',
      options: {port: 5432, host: 'localhost', user: 'postgres', password: 'password'}
    }
  }
end

[6] pry(main)> ActiveContext.adapter
=> #<ActiveContext::Databases::Postgresql::Adapter:0x000000017e6d35b0
 @client=
  #<ActiveContext::Databases::Postgresql::Client:0x0000000305997958
   @conn=#<PG::Connection:0x000000017e67df70 host=localhost port=5432 user=postgres>,
   @options={:port=>5432, :host=>"localhost", :user=>"postgres", :password=>"password"}>>
[7] pry(main)> ActiveContext.adapter.search(nil).first
=> {"datid"=>"5",
 "datname"=>"postgres",
 "pid"=>"260",
 "leader_pid"=>nil,
 "usesysid"=>"10",
 "usename"=>"postgres",
 "application_name"=>"bin/rails",
 "client_addr"=>"192.168.65.1",
 "client_hostname"=>nil,
 "client_port"=>"40909",
 "backend_start"=>"2024-12-27 14:05:35.732894+00",
 "xact_start"=>"2024-12-27 14:15:22.279428+00",
 "query_start"=>"2024-12-27 14:15:22.279428+00",
 "state_change"=>"2024-12-27 14:15:22.27944+00",
 "wait_event_type"=>nil,
 "wait_event"=>nil,
 "state"=>"active",
 "backend_xid"=>nil,
 "backend_xmin"=>"750",
 "query_id"=>nil,
 "query"=>"SELECT * FROM pg_stat_activity",
 "backend_type"=>"client backend"}

References

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• #508641 (closed)

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Related to #508641 (closed)