[SPM] Deprecate support for Spanmetrics Processor naming convention (j…

…aegertracing#4741)

## Which problem is this PR solving?
- Part 1 of jaegertracing#4736

## Description of the changes
- Add deprecation notice to CLI flag
- Add log message when using span metrics processor notation

## How was this change tested?
```
$ go run ./cmd/all-in-one help
      --prometheus.query.support-spanmetrics-connector            (deprecated, will be removed after 2024-01-01 or in release v1.53.0, whichever is later)  Controls whether the metrics queries should match the OpenTelemetry Collector's spanmetrics connector naming (when true) or spanmetrics processor naming (when false). (default true)

$ PROMETHEUS_QUERY_SUPPORT_SPANMETRICS_CONNECTOR=false METRICS_STORAGE_TYPE=prometheus go run ./cmd/all-in-one
2023/09/09 20:29:19 using Spanmetrics Processor's metrics naming conventions (deprecated, will be removed after 2024-01-01 or in release v1.53.0, whichever is later)
```

cc @albertteoh

Signed-off-by: Yuri Shkuro <[email protected]>

plugin/metrics/prometheus/options.go

@@ -17,6 +17,7 @@ package prometheus
 import (
 	"flag"
 	"fmt"
+	"log"
 	"strings"
 	"time"
 
@@ -47,6 +48,8 @@ const (
 	defaultLatencyUnit                 = "ms"
 	defaultNormalizeCalls              = false
 	defaultNormalizeDuration           = false
+
+	deprecatedSpanMetricsProcessor = "(deprecated, will be removed after 2024-01-01 or in release v1.53.0, whichever is later) "
 )
 
 type namespaceConfig struct {
@@ -91,9 +94,10 @@ func (opt *Options) AddFlags(flagSet *flag.FlagSet) {
 		"The path to a file containing the bearer token which will be included when executing queries against the Prometheus API.")
 	flagSet.Bool(nsConfig.namespace+suffixOverrideFromContext, true,
 		"Whether the bearer token should be overridden from context (incoming request)")
-
-	flagSet.Bool(nsConfig.namespace+suffixSupportSpanmetricsConnector, defaultSupportSpanmetricsConnector,
-		`Whether if queries should be adjusted for OpenTelemetry Collector's spanmetrics connector.'`)
+	flagSet.Bool(
+		nsConfig.namespace+suffixSupportSpanmetricsConnector,
+		defaultSupportSpanmetricsConnector,
+		deprecatedSpanMetricsProcessor+" Controls whether the metrics queries should match the OpenTelemetry Collector's spanmetrics connector naming (when true) or spanmetrics processor naming (when false).")
 	flagSet.String(nsConfig.namespace+suffixMetricNamespace, defaultMetricNamespace,
 		`The metric namespace that is prefixed to the metric name. A '.' separator will be added between `+
 			`the namespace and the metric name.`)
@@ -124,6 +128,9 @@ func (opt *Options) InitFromViper(v *viper.Viper) error {
 	cfg.TokenFilePath = v.GetString(cfg.namespace + suffixTokenFilePath)
 
 	cfg.SupportSpanmetricsConnector = v.GetBool(cfg.namespace + suffixSupportSpanmetricsConnector)
+	if !cfg.SupportSpanmetricsConnector {
+		log.Printf("using Spanmetrics Processor's metrics naming conventions " + deprecatedSpanMetricsProcessor)
+	}
 	cfg.MetricNamespace = v.GetString(cfg.namespace + suffixMetricNamespace)
 	cfg.LatencyUnit = v.GetString(cfg.namespace + suffixLatencyUnit)
 	cfg.NormalizeCalls = v.GetBool(cfg.namespace + suffixNormalizeCalls)