[KeyVault] - Update duration sample and doc comments (#18508)

## What

- Use Day.js in the Key Rotation sample
- Update the doc comments for Key Rotation

## Why

We discussed adding updating the API of Key Rotation to take an object instead
of a raw string for ISO8601 durations; however, with Temporal adding support for
Durations we want to avoid duplicating the type for now. Instead, we decided to
demonstrate interop with an existing 3rd party library. I chose Day.js for this
sample as it has a nice clean API.

sdk/keyvault/keyvault-keys/package.json

@@ -133,6 +133,7 @@
     "chai-as-promised": "^7.1.1",
     "chai-exclude": "^2.0.2",
     "cross-env": "^7.0.2",
+    "dayjs": "^1.10.7",
     "dotenv": "^8.2.0",
     "eslint": "^7.15.0",
     "esm": "^3.2.18",

sdk/keyvault/keyvault-keys/samples-dev/keyRotation.ts

@@ -7,6 +7,9 @@
 
 import { KeyClient } from "@azure/keyvault-keys";
 import { DefaultAzureCredential } from "@azure/identity";
+import dayjs from "dayjs";
+import duration from "dayjs/plugin/duration";
+dayjs.extend(duration);
 
 // Load the .env file if it exists
 import * as dotenv from "dotenv";
@@ -43,11 +46,15 @@ export async function main(): Promise<void> {
   console.log("fetched policy", currentPolicy);
 
   // Update the key's automated rotation policy to notify 30 days before the key expires.
+  // By using the ISO8601 duration standard, interoperability with any 3rd party library that supports Durations is supported.
+  // In this example, we'll use Day.js (documented in https://day.js.org) to create the duration.
+  // For more information on the ISO 8601 Duration standard, please refer to the Wikipedia page on Durations:
+  // https://wikipedia.org/wiki/ISO_8601#Durations
   const updatedPolicy = await client.updateKeyRotationPolicy(key.name, {
     lifetimeActions: [
       {
         action: "Notify",
-        timeBeforeExpiry: "P30D"
+        timeBeforeExpiry: dayjs.duration({ days: 30 }).toISOString()
       }
     ],
     expiresIn: "P90D"

sdk/keyvault/keyvault-keys/src/index.ts

@@ -773,6 +773,7 @@ export class KeyClient {
 
   /**
    * Gets the requested number of bytes containing random values from a managed HSM.
+   * This operation requires the managedHsm/rng permission.
    *
    * Example usage:
    * ```ts
@@ -848,11 +849,12 @@ export class KeyClient {
 
   /**
    * Gets the rotation policy of a Key Vault Key.
+   * By default, all keys have a policy that will notify 30 days before expiry.
    *
+   * This operation requires the keys/get permission.
    * Example usage:
    * ```ts
    * let client = new KeyClient(vaultUrl, credentials);
-   * await client.updateKeyRotationPolicy("MyKey", myPolicy);
    * let result = await client.getKeyRotationPolicy("myKey");
    * ```
    *
@@ -871,6 +873,7 @@ export class KeyClient {
 
   /**
    * Updates the rotation policy of a Key Vault Key.
+   * This operation requires the keys/update permission.
    *
    * Example usage:
    * ```ts