Exporter implementation

[FW-Nagorko]

This pull request introduces a new command-line interface (CLI) and inter-process communication mechanism to the agent, allowing users to start and stop metric exports via commands. It also refactors the build system and agent binary for improved usability and maintainability. The most important changes are grouped below.

Agent CLI and Export Functionality:

• Added a CLI mode to the agent (main.cc) that allows sending "export start" and "export stop" commands to the running agent process using a POSIX message queue. The agent now distinguishes between CLI and daemon modes based on the executable name, and creates a hardlink (voltad) for the daemon. [1] [2] [3]
• Implemented a MessageQueue abstraction for POSIX message queues, supporting both sender and receiver roles, with notification and message handling logic. [1] [2]
• Added an Exporter class that manages exporting collected metrics to a CSV file, with start/stop control via message queue commands. Exported metrics include device information and timestamps. [1] [2] [3]
• Integrated the exporter and message queue into the agent's Scheduler, enabling runtime control of metric export and reflecting export status in the dashboard. [1] [2] [3] [4]

Build System and Configuration:

• Renamed the agent binary and CMake target from volta_agent to volta, and updated all related references in CMakeLists.txt. Added logic to create a hardlink named voltad for agent mode. [1] [2] [3] [4]
• Added a default dump directory path (/var/lib/volta/dumps) to the agent configuration, with support for override. [1] [2]

These changes collectively enable dynamic metric export control via CLI commands, improve agent usability, and modernize the build and configuration setup.

[varev-dev]

lgtm 🚀