chore: Add processId field for metrics of threads/db-pool-stat/health (#6797)

Co-authored-by: 老潮 <zhangyongsheng@3vjia.com>
Co-authored-by: takatost <takatost@users.noreply.github.com>
Co-authored-by: takatost <takatost@gmail.com>

api/app.py

 @app.route('/health')
 def health():
     return Response(json.dumps({
+        'pid': os.getpid(),
         'status': 'ok',
         'version': app.config['CURRENT_VERSION']
     }), status=200, content_type="application/json")
         })
 
     return {
+        'pid': os.getpid(),
         'thread_num': num_threads,
         'threads': thread_list
     }
 def pool_stat():
     engine = db.engine
     return {
+        'pid': os.getpid(),
         'pool_size': engine.pool.size(),
         'checked_in_connections': engine.pool.checkedin(),
         'checked_out_connections': engine.pool.checkedout(),