feat(agent):metrics for errors in agent

[ghost]

Checklist

• I have read the coding guide.
• I have filled out the description and linked the related issues.

Description

Adds metrics for errors for Grafana dashboard

Open API Spec Version Changes (if applicable)

Motivation and Context (Optional)

An extension of Agent feature in storage incentives.

Related Issue (Optional)

NA

Screenshots (if appropriate):

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This change is 

[ghost]

@istae @vladopajic ci errs unrelated to pr

[istae]

Nice work, small suggestions :)

[istae]

rename to is_playing_errors

[vladopajic]

Ideally these should be exposed by ChainBackend interface (or any other type wrapping this interface in order to provide this this functionality.

[vladopajic]

Ideally metrics should be defined and calculated inside the same scope where logic (which is being measured) is defined.

That is, if measured function is doTask() it would be the best to put metrics inside this function

func doTask() (err error) {
	a.metrics.DoTaskCalls().Inc()
	defer func() {
		if err {
			a.metrcis.DoCallsErr().inc()
		}
	}()

	// ... 
}

Having this practice enables more robust code because code using doTask() function will not have to take care of calculating it's metrics; also it improves code reuse. For example BackendCalls should be measured inside this type, and if it is implemented this way then all other logic would have these metrics out of the box.

[ghost]

Ideally metrics should be defined and calculated inside the same scope where logic (which is being measured) is defined.

That is, if measured function is doTask() it would be the best to put metrics inside this function

func doTask() (err error) {
	a.metrics.DoTaskCalls().Inc()
	defer func() {
		if err {
			a.metrcis.DoCallsErr().inc()
		}
	}()

	// ... 
}

Having this practice enables more robust code because code using doTask() function will not have to take care of calculating it's metrics; also it improves code reuse. For example BackendCalls should be measured inside this type, and if it is implemented this way then all other logic would have these metrics out of the box.

makes sense, thankyou, will keep it in mind.