Add migration details for extension api docs (#3074)

* updating extension api docs for 5.0

Signed-off-by: Jim Ehrismann <jehrismann@mirantis.com>

* beefed up migration details

Signed-off-by: Jim Ehrismann <jehrismann@mirantis.com>

* address review comments

Signed-off-by: Jim Ehrismann <jehrismann@mirantis.com>

* updated cluster features docs (#3094)

Signed-off-by: Jim Ehrismann <jehrismann@mirantis.com>

* revert extension package-lock.json files again

Signed-off-by: Jim Ehrismann <jehrismann@mirantis.com>

docs/extensions/guides/main-extension.md

@@ -2,13 +2,14 @@
 
 The Main Extension API is the interface to Lens's main process.
 Lens runs in both main and renderer processes.
-The Main Extension API allows you to access, configure, and customize Lens data, add custom application menu items, and run custom code in Lens's main process.
+The Main Extension API allows you to access, configure, and customize Lens data, add custom application menu items and [protocol handlers](protocol-handlers.md), and run custom code in Lens's main process.
+It also provides convenient methods for navigating to built-in Lens pages and extension pages, as well as adding and removing sources of catalog entities. 
 
-## `LensMainExtension` Class
+## `Main.LensExtension` Class
 
 ### `onActivate()` and `onDeactivate()` Methods
 
-To create a main extension simply extend the `LensMainExtension` class:
+To create a main extension simply extend the `Main.LensExtension` class:
 
 ```typescript
 import { Main } from "@k8slens/extensions";
@@ -75,3 +76,27 @@ Valid values include: `"file"`, `"edit"`, `"view"`, and `"help"`.
 In this example, we simply log a message.
 However, you would typically have this navigate to a specific page or perform another operation.
 Note that pages are associated with the [`Renderer.LensExtension`](renderer-extension.md) class and can be defined in the process of extending it.
+
+The following example demonstrates how an application menu can be used to navigate to such a page:
+
+``` typescript
+import { Main } from "@k8slens/extensions";
+
+export default class SamplePageMainExtension extends Main.LensExtension {
+  appMenus = [
+    {
+      parentId: "help",
+      label: "Sample",
+      click: () => this.navigate("myGlobalPage")
+    }
+  ]
+}
+```
+
+When the menu item is clicked the `navigate()` method looks for and displays a global page with id `"myGlobalPage"`.
+This page would be defined in your extension's `Renderer.LensExtension` implmentation (See [`Renderer.LensExtension`](renderer-extension.md)).
+
+### `addCatalogSource()` and `removeCatalogSource()` Methods
+
+The `Main.LensExtension` class also provides the `addCatalogSource()` and `removeCatalogSource()` methods, for managing custom catalog items (or entities).
+See the [`Catalog`](catalog.md) documentation for full details about the catalog.