feat!: upgrade to latest stable otel API v1.21.0

otel uses a little bit of a strange versioning schema, where the
contracts are versioned under otel/semconv/{VERSION}, but the package
can be upgraded to several versions ahead of the contract. This has
worked fine for our use-cases, but we recently ran into a problem where
we go the following error on application startup - after a dependabot
upgrade came along:
```
cannot merge resource due to conflicting Schema URL
```
This led down a rabbit hole, eventually finding out this quirk in otel
usage.

BREAKING CHANGE: This upgrades the version of the otel contract being
used. This is possibly a breaking change so care must be taken so that
other OTEL packages are upgraded to v1.21 simultaneously so there aren't
further breakages.

Author: Karl Johan Ansari-Önnestam

cloudmonitoring/metricmiddleware.go

@@ -9,7 +9,7 @@ import (
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/metric"
-	semconv "go.opentelemetry.io/otel/semconv/v1.7.0"
+	semconv "go.opentelemetry.io/otel/semconv/v1.21.0"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"

cloudotel/metricexporter.go

@@ -17,7 +17,7 @@ import (
 	"go.opentelemetry.io/otel/sdk/instrumentation"
 	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
 	"go.opentelemetry.io/otel/sdk/resource"
-	semconv "go.opentelemetry.io/otel/semconv/v1.14.0"
+	semconv "go.opentelemetry.io/otel/semconv/v1.21.0"
 	"go.uber.org/zap"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
@@ -73,7 +73,7 @@ func StartMetricExporter(
 				"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp",
 				semconv.NetPeerPortKey,
 				semconv.NetSockPeerPortKey,
-				semconv.HTTPClientIPKey,
+				attribute.Key("http.client_ip"),
 			),
 			maskInstrumentAttrs(
 				"go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc",

go.mod

@@ -42,7 +42,7 @@ require (
 	cloud.google.com/go/compute v1.23.3 // indirect
 	cloud.google.com/go/monitoring v1.16.3 // indirect
 	cloud.google.com/go/trace v1.10.4 // indirect
-	github.com/GoogleCloudPlatform/opentelemetry-operations-go/detectors/gcp v1.20.0 // indirect
+	github.com/GoogleCloudPlatform/opentelemetry-operations-go/detectors/gcp v1.21.0 // indirect
 	github.com/GoogleCloudPlatform/opentelemetry-operations-go/internal/resourcemapping v0.45.0 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
 	github.com/go-logr/logr v1.3.0 // indirect

go.sum

@@ -22,8 +22,8 @@ cloud.google.com/go/storage v1.30.1/go.mod h1:NfxhC0UJE1aXSx7CIIbCf7y9HKT7Biccwk
 cloud.google.com/go/trace v1.10.4 h1:2qOAuAzNezwW3QN+t41BtkDJOG42HywL73q8x/f6fnM=
 cloud.google.com/go/trace v1.10.4/go.mod h1:Nso99EDIK8Mj5/zmB+iGr9dosS/bzWCJ8wGmE6TXNWY=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
-github.com/GoogleCloudPlatform/opentelemetry-operations-go/detectors/gcp v1.20.0 h1:tk85AYGwOf6VNtoOQi8w/kVDi2vmPxp3/OU2FsUpdcA=
-github.com/GoogleCloudPlatform/opentelemetry-operations-go/detectors/gcp v1.20.0/go.mod h1:Xx0VKh7GJ4si3rmElbh19Mejxz68ibWg/J30ZOMrqzU=
+github.com/GoogleCloudPlatform/opentelemetry-operations-go/detectors/gcp v1.21.0 h1:aNyyrkRcLMWFum5qgYbXl6Ut+MMOmfH/kLjZJ5YJP/I=
+github.com/GoogleCloudPlatform/opentelemetry-operations-go/detectors/gcp v1.21.0/go.mod h1:BEOBnuYVyPt9wxVRQqqpKUK9FXVcL2+LOjZ8apLa9ao=
 github.com/GoogleCloudPlatform/opentelemetry-operations-go/exporter/metric v0.45.0 h1:Oh5/2grZuv8p5+lidwW2ZfT3V/A3uGS0VaffKDQuOco=
 github.com/GoogleCloudPlatform/opentelemetry-operations-go/exporter/metric v0.45.0/go.mod h1:P+p6V+38uic90/V32zbCutZOcZxzvKjSQX2M1BFMopo=
 github.com/GoogleCloudPlatform/opentelemetry-operations-go/exporter/trace v1.21.0 h1:OEgjQy1rH4Fbn5IpuI9d0uhLl+j6DkDvh9Q2Ucd6GK8=