Add padding for FooterHelp on small devices (#11299)

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### WHY are these changes introduced?

The missing padding for `FooterHelp` leads to the text being completely
at the edge of a screen on small devices. This doesn't happen on md and
up. It's imho surprising to remove a padding for small screens and leads
to issues in Web Admin.

| Before | After |
| - | - |
|
![image](https://github.com/Shopify/polaris/assets/9371695/35d1f83d-a82f-40db-93e8-56e1c1d0db88)
|
![image](https://github.com/Shopify/polaris/assets/9371695/155671ad-9b3c-46b9-a996-3bc5c644b6d8)
|

<!--
  Context about the problem that’s being addressed.
-->

### WHAT is this pull request doing?

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It unifies the padding for `FooterHelp` across all breakpoints.

### How to 🎩

- Go to `FooterHelp` story
- Ensure the padding is applied regardless of the size of the screen.

🖥 [Local development
instructions](https://github.com/Shopify/polaris/blob/main/README.md#install-dependencies-and-build-workspaces)
🗒 [General tophatting
guidelines](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting.md)
📄 [Changelog
guidelines](https://github.com/Shopify/polaris/blob/main/.github/CONTRIBUTING.md#changelog)

### 🎩 checklist

- [ ] Tested a
[snapshot](https://github.com/Shopify/polaris/blob/main/documentation/Releasing.md#-snapshot-releases)
- [x] Tested on
[mobile](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting.md#cross-browser-testing)
- [x] Tested on [multiple
browsers](https://help.shopify.com/en/manual/shopify-admin/supported-browsers)
- [x] Tested for
[accessibility](https://github.com/Shopify/polaris/blob/main/documentation/Accessibility%20testing.md)
- [x] Updated the component's `README.md` with documentation changes
- [x] [Tophatted
documentation](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting%20documentation.md)
changes in the style guide

.changeset/calm-berries-tie.md

@@ -0,0 +1,5 @@
+---
+'@shopify/polaris': patch
+---
+
+Added padding for FooterHelp on small viewports

polaris-react/src/components/FooterHelp/FooterHelp.scss

@@ -3,13 +3,8 @@
 .FooterHelp {
   display: flex;
   justify-content: center;
-  margin: var(--p-space-500) 0;
-  width: 100%;
-
-  @media #{$p-breakpoints-sm-up} {
-    margin: var(--p-space-500);
-    width: auto;
-  }
+  margin: var(--p-space-500);
+  width: auto;
 }
 
 .Text {