metrics: seperate metrics with source scope for txn command

[cfzjywxk]

ref: pingcap/tidb#41203

Add source scope for several metrics.

The grafana change result would be posted latter, related PR would be opened in the tidb repo.

[you06]

And may change the implementation of KVTxn.isInternal and KVSnapshot.IsInternal to inherit IsInternal from RequestSource.

func (r *RequestSource) IsInternal() bool {
	if r == nil {
		return false
	}
	return r.RequestSourceInternal
}

[you06]

TxnRegionsNumHistogramWithCoprocessorInternal is missing

[you06]

The type "coprocessor" is wrong, and the init of TxnRegionsNumHistogramWithCoprocessor and TxnRegionsNumHistogramWithCoprocessorInternal is missing.

[you06]

Suggested change

	isInternalReq := util.IsInternalRequest(c.txn.GetRequestSource())
	isInternalReq := c.txn.isInternal()

[you06]

TxnWriteKVCountHistogramInternal and TxnWriteKVCountHistogramGeneral are not initialized.

Unluckily there is no codegen by macro for such works :(

[cfzjywxk]

Missing TxnWriteSizeHistogramInternal and TxnWriteSizeHistogramGeneral are added.

[cfzjywxk]

And may change the implementation of KVTxn.isInternal and KVSnapshot.IsInternal to inherit IsInternal from RequestSource.

func (r *RequestSource) IsInternal() bool {
	if r == nil {
		return false
	}
	return r.RequestSourceInternal
}

@you06
There's a method wrapped in https://github.com/tikv/client-go/blob/master/util/request_source.go#L64, I think it's better to check nil first and void using nil references.

[you06]

@

There's a method wrapped in https://github.com/tikv/client-go/blob/master/util/request_source.go#L64, I think it's better to check nil first and void using nil references.

Yes the nil check is required, what I mean is to avoid making string and check it, we can check RequestSource.RequestSourceInternal directly if possible. The function IsInternalRequest is used when we have request context, the request source is formatted as a string in it.

[cfzjywxk]

@you06
Got it, I've changed the util.IsRequestSourceInternal implementation to use the boolean RequestSourceInternal directly.