[BREAKING CHANGE] Enable "new-metrics" by default

[pjanotti]

Description:
This change switches the defaults between "new-metrics" and "legacy-metrics".

Now the defaults are:

• "new-metrics" ON by default
• "legacy-metrics" OFF by default
• "add-instance-id" ON by default

Link to tracking Issue: Third item on #1082

Testing: Added test to enforce the "service_instance_id" label ON by default.

Documentation: Updated monitoring.md to reflect that the "new-metrics" are on by default.

[pjanotti]

@nilebox @rghetia let's not merge this one until you give the thumbs up.

[codecov]

Codecov Report

Merging #1148 into master will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1148      +/-   ##
==========================================
- Coverage   86.86%   86.84%   -0.02%     
==========================================
  Files         201      201              
  Lines       14521    14521              
==========================================
- Hits        12613    12611       -2     
- Misses       1458     1459       +1     
- Partials      450      451       +1     

Impacted Files	Coverage Δ
internal/collector/telemetry/telemetry.go	87.93% <100.00%> (ø)
translator/internaldata/resource_to_oc.go	73.52% <0.00%> (-2.95%)	⬇️
service/service.go	52.06% <0.00%> (ø)

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[nilebox]

@pjanotti thanks for waiting for the feedback from Google.
This change should be fine to merge, and we can still override default flags via explicitly enabling "legacy mode" if needed.

We do have custom observability extensions (we use a custom exporter instead of Prometheus there) using the "legacy views" though, e.g.

opentelemetry-collector/observability/observability.go

Lines 69 to 70 in e3df9f3

	// ViewReceiverReceivedTimeSeries defines the view for the receiver received timeseries metric.
	var ViewReceiverReceivedTimeSeries = &view.View{

As far as I understand, the plan is to delete these legacy views completely, so we will need to migrate our custom extensions to using new views instead. The issue here is that the new metric views are being generated dynamically in private function

opentelemetry-collector/obsreport/obsreport.go

Line 111 in e3df9f3

func genAllViews() (views []*view.View) {

, so we need to make these views accessible outside of the obsreport package, e.g. we should be able to reference a view for measure

opentelemetry-collector/obsreport/obsreport_receiver.go

Line 61 in e3df9f3

mReceiverAcceptedSpans = stats.Int64(

[tigrannajaryan]

@rghetia @mtwo can we get one more +1 from Google? We want to make sure this is not breaking anything for you.

[pjanotti]

@nilebox Thanks for reviewing.

As far as I understand, the plan is to delete these legacy views completely, so we will need to migrate our custom extensions to using new views instead. The issue here is that the new metric views are being generated dynamically in private function, so we need to make these views accessible outside of the obsreport package, e.g. we should be able to reference a view for measure

Yes, the plan is to eventually completely remove the legacy views but that should be the very last step. I don't see any problem exposing the obsreport views (I didn't expose them initially since I didn't have a reason to do so).

[rghetia]

LGTM.