chore: update readme about version support (#10691)

Starting in 2025 these libraries will support just two versions of Go. This is a similar policy used by the Go programming language and many of our dependencies with the addition of GOTOOLCHAIN which was added in 1.21.

This policy has also been announced here: https://cloud.google.com/go/getting-started/supported-go-versions

Also unfreeze some deps now that we support 1.21.

.github/renovate.json

@@ -13,14 +13,7 @@
     "commitMessageAction": "update",
     "groupName": "deps",
     "ignoreDeps": [
-        "github.com/GoogleCloudPlatform/opentelemetry-operations-go/exporter/trace",
-        "go.opentelemetry.io/contrib/detectors/gcp",
-        "go.opentelemetry.io/otel",
-        "go.opentelemetry.io/otel/metric",
-        "go.opentelemetry.io/otel/sdk",
-        "go.opentelemetry.io/otel/trace",
-        "google.golang.org/genproto",
-        "google.golang.org/grpc"
+        "google.golang.org/genproto"
     ],
     "ignorePaths": [
         "**/snippets/**"
@@ -37,7 +30,7 @@
     ],
     "force": {
         "constraints": {
-            "go": "1.20"
+            "go": "1.21"
         }
     }
 }

README.md

@@ -28,12 +28,16 @@ For an updated list of all of our released APIs please see our
 
 ## [Go Versions Supported](#supported-versions)
 
+**Note:** As of Jan 1, 2025 the Cloud Client Libraries for Go will support the
+two most-recent major Go releases -- the same [policy](https://go.dev/doc/devel/release#policy)
+the Go programming language follows.
+
 Our libraries are compatible with at least the three most recent, major Go
 releases. They are currently compatible with:
 
+- Go 1.23
 - Go 1.22
 - Go 1.21
-- Go 1.20
 
 ## Authorization