doc: add feature flag guidelines (#7951)

Signed-off-by: Mariam Fahmy <mariam.fahmy@nirmata.com>

docs/dev/feature-flags/README.md

@@ -0,0 +1,60 @@
+# Feature Flags Guidelines
+## Introduction
+Feature flags, also known as feature toggles, are a software development technique that allows developers to turn features on and off in a production environment without requiring a new deployment.
+
+There are several ways to enable/disable features in Golang:
+1. Feature Toggles: It provides a simple way to enable/disable features based on environment variables and/or command line arguments
+2. Container arguments
+
+## Feature Flags
+The `toggle` package exists in pkg/toggle can be used to define and manage a feature toggle for a new feature in Kyverno. Lets say we need to introduce a new feature toggle to enable/disable deferred loading. We can do it as follows:
+1. Define a flag name, description, environment variable and a default value for this new feature in the `toggle` package:
+    ```
+    EnableDeferredLoadingFlagName    = "enableDeferredLoading"
+    EnableDeferredLoadingDescription = "enable deferred loading of context variables"
+    enableDeferredLoadingEnvVar      = "FLAG_ENABLE_DEFERRED_LOADING"
+    defaultEnableDeferredLoading     = true
+    ``` 
+2. Create a new toggle for the new feature using the `newToggle` method which takes both default value and environment variable as arguments:
+    ```
+    EnableDeferredLoading    = newToggle(defaultEnableDeferredLoading, enableDeferredLoadingEnvVar)
+    ```
+    
+    At this point, we have an instance of `toggle` which will be used later to call `toggle.enabled()` of the feature toggle to execute code conditionally. 
+
+3. Add a new method `EnableDeferredLoading() bool` in `Toggles` Interface at pkg/toggle/context.go to call the `enabled` method. It will be used later in Kyverno controllers:
+   ```
+   type Toggles interface {
+       EnableDeferredLoading() bool
+   }
+
+   func (defaultToggles) EnableDeferredLoading() bool {
+	   return EnableDeferredLoading.enabled()
+   }
+   ```
+
+4. In the controller, we can use it as follows:
+   
+   ```
+   flag.Func(toggle.EnableDeferredLoadingFlagName, toggle.EnableDeferredLoadingDescription, toggle.EnableDeferredLoading.Parse)
+   ```
+
+### Advantages
+1. Feature toggles can be accessed globally. Its value can be checked anywhere in the code, no need to pass it as an argument among methods/functions.
+
+2. Users can either enable/disable the feature by setting it as an argument to the container `--enableDeferredLoading=false` or setting its
+environment variable `FLAG_ENABLE_DEFERRED_LOADING=0`
+
+## Container Arguments
+Container arguments can be used directly in the controller. Lets say we want to add a new container flag `--enable-feature`, we can do it as follows:
+1. Create a variable for this new flag:
+```
+var(
+    enableFeature bool
+)
+```
+
+2. Define a bool flag with specified name, default value, and usage:
+```
+flagset.BoolVar(&enableFeature, "enable-feature", true, "Set this flag to 'false' to ....")
+```