Add `container_scanning` directive in agent config file and deprecate `starboard` directive

Problem to solve

Considering that we are no longer using Starboard for Operational Container Scanning, it no longer makes sense to use term starboard in the agent config file.

Proposal

1. The term container_scanning will be added as an alternate option instead of using the term starboard in the definition for the agent config file.
   1. Note: We we will continue to support starboard in the code through %16.0 as this will be a breaking change.
2. Documentation will be updated to reflect this change.

Implementation Plan

• Update agentcfg.proto to add container_scanning similar to starboard
• Update internal/module/starboard_vulnerability/agent/module.go to get container_scanning from agentcfg.AgentConfiguration and if it's empty fallback to starboard
• [-] For consistency, update the name of the directory from internal/module/starboard_vulnerability to internal/module/container_scanning and update the references
• documentation Update documentation to mention the starboard field will not be supported from %16.0