bug: apisix-dashboard unable to set upstream.pass_host as node when node more than 1

[leslie-tsang]

Issue description

I found code below in apisix-dashboard make it unable to select Use the domain or IP from Node List in Hostname, Which apisix had supported.

apisix-dashboard/web/src/components/Upstream/components/PassHost.tsx

Lines 88 to 102 in 9764dad

	if (
	form.getFieldValue('pass_host') === 'node' &&
	(form.getFieldValue('nodes') || []).length !== 1
	) {
	notification.warning({
	message: formatMessage({
	id: 'component.upstream.other.pass_host-with-multiple-nodes.title',
	}),
	description: formatMessage({
	id: 'component.upstream.other.pass_host-with-multiple-nodes',
	}),
	});
	form.setFieldsValue({ pass_host: 'pass' });
	}
	return null;

payload below supported by apisix

{
        "uri": "/route-test",
        "name": "route-test",
        "upstream": {
          "pass_host": "node",
          "hash_on": "vars",
          "nodes": {
                "web1:80": 1,
                "web2:80": 1
          },
          "type": "roundrobin",
          "retries": 2,
          "checks": {
              "active": {
                  "timeout": 1,
                  "http_path": "/",
                  "healthy": {
                      "http_statuses": [200, 201, 302],
                      "interval": 1,
                      "successes": 1
                  },
                  "unhealthy": {
                      "http_statuses": [429,404,500,501,502,503,504,505],
                      "interval": 1,
                      "timeout": 1,
                      "http_failures": 1
                  }
              },
              "passive": {
                 "healthy": {
                    "http_statuses": [200, 201, 302],
                    "successes": 1
                 },
                 "unhealthy": {
                    "http_statuses": [429,404,500,501,502,503,504,505],
                    "http_failures": 1,
                    "tcp_failures": 1
                }
              }
          }
    }
}

Expected behavior

apisix-dashboard support upstream.pass_host as node when node list lager than 1

How to Reproduce

1. Open the apisix-dashboard
2. Create a new route rule
3. Define API Backend Server
4. Add more than 1 node in target list
5. Change Hostname to Use the domain or IP from Node List
6. apisix-dashboard will show a alert of When using a host name or IP in the target node list, make sure there is only one target node

Screenshots

No response

Environment

• apisix version (cmd: apisix version): 2.9
• OS (cmd: uname -a): Linux localhost 3.10.0-1160.el7.x86_64 SMP Mon Oct 19 16:18:59 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
• OpenResty / Nginx version (cmd: nginx -V or openresty -V): 1.19.9.1
• etcd version, if have (cmd: run etcd --version): 3.4.15
• apisix-dashboard version, if have: 2.8
• Browser version, if have: latest Chrome

Additional context

No response