server/internal/client/ollama: set User-Agent for registry client (#9775)

This sets the agent header in DefaultRegistry to include the version of
the client, OS, and architecture in the previous format, with a minor
twist.

Note: The version is obtained from the build info, instead of the
version in version.Version, which should not longer be necessary, but we
can remove in a future commit. Using the build info is more accurate and
also provides extra build information if the build is not tagged, and if
it is "dirty". Previously, the version was just "0.0.0" with no other
helpful information. The ollama.com registry and others handle this
swimmingly.

server/internal/client/ollama/registry.go

@@ -25,6 +25,7 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
+	"runtime/debug"
 	"slices"
 	"strconv"
 	"strings"
@@ -259,6 +260,7 @@ func DefaultRegistry() (*Registry, error) {
 	}
 
 	var rc Registry
+	rc.UserAgent = UserAgent()
 	rc.Key, err = ssh.ParseRawPrivateKey(keyPEM)
 	if err != nil {
 		return nil, err
@@ -274,6 +276,16 @@ func DefaultRegistry() (*Registry, error) {
 	return &rc, nil
 }
 
+func UserAgent() string {
+	buildinfo, _ := debug.ReadBuildInfo()
+	return fmt.Sprintf("ollama/%s (%s %s) Go/%s",
+		buildinfo.Main.Version,
+		runtime.GOARCH,
+		runtime.GOOS,
+		runtime.Version(),
+	)
+}
+
 func (r *Registry) maxStreams() int {
 	return cmp.Or(r.MaxStreams, runtime.GOMAXPROCS(0))
 }