Improve the default JSON rule parsers in ext/datasource package

[sczyh30]

Issue Description

Type: improvement

Describe what feature you want

The default JSON rule parsers in ext/datasource package could be improved. In current implementation, even if the JSON itself is not an array of flow rule entities, empty FlowRule might be generated:

sentinel-golang/ext/datasource/helper.go

Lines 32 to 51 in 1f1c71b

	rules := make([]*flow.FlowRule, 0)
	result := gjson.ParseBytes(src)
	for _, r := range result.Array() {
	flowRule := &flow.FlowRule{
	Resource: r.Get("resource").String(),
	LimitOrigin: r.Get("limitOrigin").String(),
	MetricType: flow.MetricType(r.Get("metricType").Int()),
	Count: r.Get("count").Float(),
	RelationStrategy: flow.RelationStrategy(r.Get("relationStrategy").Int()),
	ControlBehavior: flow.ControlBehavior(r.Get("controlBehavior").Int()),
	RefResource: r.Get("refResource").String(),
	WarmUpPeriodSec: uint32(r.Get("warmUpPeriodSec").Int()),
	MaxQueueingTimeMs: uint32(r.Get("maxQueueingTimeMs").Int()),
	ClusterMode: r.Get("clusterMode").Bool(),
	ClusterConfig: flow.ClusterRuleConfig{
	ThresholdType: flow.ClusterThresholdMode(r.Get("clusterConfig.thresholdType").Int()),
	},
	}
	rules = append(rules, flowRule)
	}

Though the empty entity will be filtered out when pumping it to downstream consumers, the creation of the "invalid" entity seems useless. In addition, it might be better to leverage the unified quotes of the fields (aka. json:"xxx") to parse the object instead of writing the logic manually.

The naming could be improved as well. For example: FlowRulesJsonConverter can be FlowRuleJsonArrayParser or other better.

Additional context

Add any other context or screenshots about the feature request here.

[binbin0325]

I'll try to work it out

[sczyh30]

cc @louyuting Any suggestions?

[louyuting]

In current implementation, even if the JSON itself is not an array of flow rule entities, empty FlowRule might be generated:

Maybe we could check the validity after parsing entity.

Naming improvement make sense.