docs(golang-sdk): Update go sdk docs (#2899)

docs/docs/clients/server-side.md

@@ -267,13 +267,11 @@ $flagsmith = new Flagsmith('<FLAGSMITH_SERVER_SIDE_ENVIRONMENT_KEY>');
 
 ```go
 import (
-  flagsmith "github.com/Flagsmith/flagsmith-go-client"
+  "os"
+  flagsmith "github.com/Flagsmith/flagsmith-go-client/v3"
 )
-ctx, cancel := context.WithCancel(context.Background())
-defer cancel()
-
 // Initialise the Flagsmith client
-client := flagsmith.NewClient('<FLAGSMITH_SERVER_SIDE_ENVIRONMENT_KEY>', flagsmith.WithContext(ctx),)
+client := flagsmith.NewClient(os.Getenv("FLAGSMITH_ENVIRONMENT_KEY"))
 ```
 
 </TabItem>
@@ -387,7 +385,7 @@ $flags->getFeatureValue('secret_button');
 
 ```go
 // The method below triggers a network request
-flags, _ := client.GetEnvironmentFlags()
+flags, _ := client.GetEnvironmentFlags(ctx)
 showButton, _ := flags.IsFeatureEnabled("secret_button")
 buttonData, _ := flags.GetFeatureValue("secret_button")
 ```
@@ -517,7 +515,7 @@ trait := flagsmith.Trait{TraitKey: "trait", TraitValue: "trait_value"}
 traits = []*flagsmith.Trait{&trait}
 
 // The method below triggers a network request
-flags, _ := client.GetIdentityFlags(identifier, traits)
+flags, _ := client.GetIdentityFlags(ctx, identifier, traits)
 
 showButton, _ := flags.IsFeatureEnabled("secret_button")
 buttonData, _ := flags.GetFeatureValue("secret_button")
@@ -689,12 +687,17 @@ $flagsmith = (new Flagsmith('<FLAGSMITH_SERVER_SIDE_ENVIRONMENT_KEY>'))
 <TabItem value="go" label="Go">
 
 ```go
-func defaultFlagHandler(featureName string) flagsmith.Flag {
-	return flagsmith.Flag{IsDefault: true, FeatureName: featureName, Value: `{"colour": "#ababab"}`}
+func DefaultFlagHandler(featureName string) (flagsmith.Flag, error) {
+	return flagsmith.Flag{
+		FeatureName: featureName,
+		IsDefault:   true,
+		Value:       `{"colour": "#FFFF00"}`,
+		Enabled:     true,
+	}, nil
 }
 
 client := flagsmith.NewClient(os.Getenv("FLAGSMITH_API_KEY"),
-		flagsmith.WithDefaultHandler(defaultFlagHandler),
+		flagsmith.WithDefaultHandler(DefaultFlagHandler),
 )
 
 ```
@@ -1239,7 +1242,7 @@ client := flagsmith.NewClient(os.Getenv("FLAGSMITH_API_KEY"),
         // Controls which mode to run in; local or remote evaluation.
         // See the `SDKs Overview Page` for more info
         // Defaults to False
-        flagsmith.WithLocalEvaluation(),
+        func WithLocalEvaluation(ctx context.Context),
 
         // The network timeout in seconds.
         flagsmith.WithRequestTimeout(10*time.Second),
@@ -1251,7 +1254,7 @@ client := flagsmith.NewClient(os.Getenv("FLAGSMITH_API_KEY"),
 
         // Controls whether Flag Analytics data is sent to the Flagsmith API
         // See https://docs.flagsmith.com/advanced-use/flag-analytics
-        flagsmith.WithAnalytics(),
+        flagsmith.WithAnalytics(ctx),
 
         // Sets `resty.Client` options.  `SetRetryCount` and `SetRetryWaitTime`
         // Ref: https://pkg.go.dev/github.com/go-resty/resty/v2#Client.SetRetryCount
@@ -1270,8 +1273,16 @@ client := flagsmith.NewClient(os.Getenv("FLAGSMITH_API_KEY"),
         // response
         flagsmith.WithDefaultHandler(defaultFlagHandler),
 
-        // You can specify the context to use.
-        flagsmith.WithContext(ctx),
+        // Allows the client to use any logger that implements the `Logger` interface.
+        flagsmith.WithLogger(ctx),
+
+        // WithProxy returns an Option function that sets the proxy(to be used by internal resty client).
+        // The proxyURL argument is a string representing the URL of the proxy server to use, e.g. "http://proxy.example.com:8080".
+        func WithProxy(proxyURL string) Option {
+            return func(c *Client) {
+                c.client.SetProxy(proxyURL)
+            }
+        }
 )
 ```