Fix Go telemetry examples: NewClient takes *ClientOptions and returns one value (#2086)

The Go OpenTelemetry example bound two return values and passed
ClientOptions by value, so copying it into a program failed to compile with
an assignment mismatch and a pointer type error.

NewClient is declared as `func NewClient(options *ClientOptions) *Client`:
it takes a pointer and returns no error. Errors surface later from Start
and CreateSession.

Correct the three duplicated copies of the snippet to the single-return
pointer form already used by NewClient's own doc comment.

Co-authored-by: examon <examon@users.noreply.github.com>

Author: examon

docs/getting-started.md

@@ -2158,7 +2158,7 @@ Install with telemetry extras: `pip install copilot-sdk[telemetry]` (provides `o
 
 <!-- docs-validate: skip -->
 ```go
-client, err := copilot.NewClient(copilot.ClientOptions{
+client := copilot.NewClient(&copilot.ClientOptions{
     Telemetry: &copilot.TelemetryConfig{
         OTLPEndpoint: "http://localhost:4318",
     },

docs/observability/opentelemetry.md

@@ -43,7 +43,7 @@ client = CopilotClient(
 
 <!-- docs-validate: skip -->
 ```go
-client, err := copilot.NewClient(copilot.ClientOptions{
+client := copilot.NewClient(&copilot.ClientOptions{
     Telemetry: &copilot.TelemetryConfig{
         OTLPEndpoint: "http://localhost:4318",
     },

go/README.md

@@ -646,7 +646,7 @@ session, err := client.CreateSession(context.Background(), &copilot.SessionConfi
 The SDK supports OpenTelemetry for distributed tracing. Provide a `Telemetry` config to enable trace export and automatic W3C Trace Context propagation.
 
 ```go
-client, err := copilot.NewClient(copilot.ClientOptions{
+client := copilot.NewClient(&copilot.ClientOptions{
     Telemetry: &copilot.TelemetryConfig{
         OTLPEndpoint: "http://localhost:4318",
     },