Add Metrics to the sync manager

[evanfoster]

Description

This PR adds metrics to the new sync manager component. I've tried to find the metrics that will allow us to identify/meaningfully alert on issues with the sync manager, but I haven't had much experience with implementing metrics—Please question any choices I've made if the motivation behind them isn't clear.

Additionally, I may need some help getting the unit tests to run correctly. Right now, the monitoring/manager/metrics_test.go tests seem to run far more often than they should, and they don't seem to run under the correct package.

[aalexandru]

overall looks good!

[aalexandru]

@evanfoster I tried to run all the tests under /pkg/monitoring and they seem to be running fine:

❯ go test -race ./pkg/monitoring/... -count=1 -v
=== RUN   TestNewMetrics
--- PASS: TestNewMetrics (0.00s)
=== RUN   TestMetricsRegistered
--- PASS: TestMetricsRegistered (0.00s)
=== RUN   TestRecordStatusErrorCnt
--- PASS: TestRecordStatusErrorCnt (0.00s)
=== RUN   TestRecordEgressRequestCnt
--- PASS: TestRecordEgressRequestCnt (0.00s)
=== RUN   TestRecordEgressRequestDur
--- PASS: TestRecordEgressRequestDur (0.00s)
=== RUN   TestRecordIngressRequestCnt
--- PASS: TestRecordIngressRequestCnt (0.00s)
=== RUN   TestRecordIngressRequestDur
--- PASS: TestRecordIngressRequestDur (0.00s)
PASS
ok  	github.com/adobe/cluster-registry/pkg/monitoring/apiserver	1.573s
=== RUN   TestNewMetrics
--- PASS: TestNewMetrics (0.00s)
=== RUN   TestInit
--- PASS: TestInit (0.00s)
=== RUN   TestRecordEgressRequestCnt
--- PASS: TestRecordEgressRequestCnt (0.00s)
=== RUN   TestRecordEgressRequestDur
--- PASS: TestRecordEgressRequestDur (0.00s)
PASS
ok  	github.com/adobe/cluster-registry/pkg/monitoring/client	2.080s
=== RUN   TestNewMetrics
--- PASS: TestNewMetrics (0.00s)
=== RUN   TestInit
--- PASS: TestInit (0.00s)
=== RUN   TestRecordRequeueCnt
--- PASS: TestRecordRequeueCnt (0.00s)
=== RUN   TestRecordReconciliationCnt
--- PASS: TestRecordReconciliationCnt (0.00s)
=== RUN   TestRecordReconciliationDur
--- PASS: TestRecordReconciliationDur (0.00s)
=== RUN   TestRecordEnqueueCnt
--- PASS: TestRecordEnqueueCnt (0.00s)
=== RUN   TestRecordEnqueueDur
--- PASS: TestRecordEnqueueDur (0.00s)
=== RUN   TestRecordErrCnt
--- PASS: TestRecordErrCnt (0.00s)
PASS
ok  	github.com/adobe/cluster-registry/pkg/monitoring/manager	2.588s

What issues are you seeing when running these tests? And what do you mean by "seem to run far more often than they should, and they don't seem to run under the correct package"?

[evanfoster]

@aalexandru I just thought i was seeing my tests run more frequently than I thought they should have. I'm not very good at parsing the output of Go's unit testing, so it's probably just a brain fart on my part.