[Page] Add compactTitle prop

[alololox]

WHY are these changes introduced?

There are multiple locations within the new markets section of the admin application where we render a Page component without spacing between the title and subtitle props:

WHAT is this pull request doing?

Adds a compactTitle prop that appends a new class, SubtitleCompact, which removes the top margin.

Copy-paste this code in playground/Playground.tsx:

import React from 'react';
import {Page} from '../src';

export function Playground() {
  return (
    <Page title="Title" subtitle="Subtitle" compactTitle>
      <p>Test text</p>
    </Page>
  );
}

How to 🎩

🖥 Local development instructions
🗒 General tophatting guidelines
📄 Changelog guidelines

🎩 checklist

• Tested on mobile
• Tested on multiple browsers
• Tested for accessibility
• Updated the component's README.md with documentation changes
• Tophatted documentation changes in the style guide
• For visual design changes, ping @ sarahill to update the Polaris UI kit

[github-actions]

size-limit report

Path	Size
cjs	163.46 KB (+0.02% 🔺)
esm	96.19 KB (+0.04% 🔺)
esnext	143.09 KB (+0.05% 🔺)
css	34.52 KB (+0.02% 🔺)

[Flufd]

I think this could be just &.compact as it's a variation of the SubTitle
See https://github.com/Shopify/polaris-react/blob/275b9dc329104a75a48bfbd7b35bed57fa24788d/src/components/Button/Button.scss

[benkovy]

Looks good to me