docs: Add onLoad event to CldImage documentation (#538)

# Description

<!-- Include a summary of the change made and also list the dependencies
that are required if any -->

## Issue Ticket Number

Fixes #497 

## Type of change

<!-- Please select all options that are applicable. -->

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [x] Fix or improve the documentation
- [ ] This change requires a documentation update


# Checklist

<!-- These must all be followed and checked. -->

- [x] I have followed the contributing guidelines of this project as
mentioned in [CONTRIBUTING.md](/CONTRIBUTING.md)
- [x] I have created an
[issue](https://github.com/cloudinary-community/next-cloudinary/issues)
ticket for this PR
- [x] I have checked to ensure there aren't other open [Pull
Requests](https://github.com/cloudinary-community/next-cloudinary/pulls)
for the same update/change?
- [x] I have performed a self-review of my own code
- [x] I have run tests locally to ensure they all pass
- [x] I have commented my code, particularly in hard-to-understand areas
- [x] I have made corresponding changes needed to the documentation

docs/pages/cldimage/configuration.mdx

@@ -1914,6 +1914,12 @@ version="1234"
       example: () => (<code>{`(event) => {}`}</code>),
       more: () => (<a className="whitespace-nowrap" href="https://nextjs.org/docs/pages/api-reference/components/image#onerror">More Info</a>)
     },
+    {
+      prop: 'onLoad',
+      type: 'function',
+      example: () => (<code>{`(event) => {}`}</code>),
+      more: () => (<a className="whitespace-nowrap" href="https://nextjs.org/docs/pages/api-reference/components/image#onload">More Info</a>)
+    },
     {
       prop: 'ref',
       type: 'ref',
@@ -1933,13 +1939,26 @@ until it's available, then force refresh the image instance in the DOM.
 **Examples**
 
 ```jsx copy
-onError={() => {
+onError={(e) => {
   alert('Image failed to load!')
 }}
 ```
 
 [Learn more about onError](https://nextjs.org/docs/pages/api-reference/components/image#onerror) on the Next.js docs.
 
+#### `onLoad`
+
+Callback that fires when an image loads completely and any [placeholder](/guides/placeholders) has been removed.
+
+**Examples**
+
+```jsx copy
+onLoad((e) => {
+  alert("Image has loaded!")
+})
+```
+
+[Learn more about onLoad](https://nextjs.org/docs/pages/api-reference/components/image#onload) on the Next.js docs.
 
 #### `ref`