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 }}

```

[optional *Relevant Links*:]
>Any extra documentation required to understand the issue.