Optimize the connection between Envoy and gateway to ensure the reliability of the connection

Description:

Add the upstream_connection_options in the bootstrap configuration to ensure the reliability of the connection

static_resources:
  clusters:
  - connect_timeout: 10s
    upstream_connection_options:
      tcp_keepalive:
        keepalive_time: 300
    load_assignment:
      cluster_name: xds_cluster
      endpoints:
      - lb_endpoints:
        - endpoint:
            address:
              socket_address:
                address: {{ .XdsServer.Address }}
                port_value: {{ .XdsServer.Port }}

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