feat(dkron-executor-shell): some improvement

[cobolbaby]

The improvements comprise:

• fix: cmd.Process.Kill() does not clean up the started process, causing the job to remain running. #1385
• refactor: Replace dependent class library github.com/struCoder/pidusage with github.com/shirou/gopsutil/v3/process
• fix: The metric dkron_job_mem_usage_kb now exclusively calculates the memory usage of the task startup process, excluding resource usage from child processes spawned by the task startup process.
• feat: Introduce two new metrics, dkron_job_execution_time_seconds and dkron_job_execution_done_count, for improved monitoring and alerting capabilities.
• fix: Should output.TotalWritten be judged after cmd.Wait() is executed? #1319
• fix: The metrics exposed by dkron are only of summary type and cannot cover related analysis for specific jobs. #1310

[vcastellm]

LGTM