fix(css): Restore paragraph spacing in parameter descriptions and response descriptions

[hkosova]

Description

See the before/after screenshots. The issue was that multi-paragraph descriptions in parameters and responses had no space between the paragraphs. (But operation descriptions have proper paragraph spacing.)

I tracked down the issue to these rules:

swagger-ui/src/style/_table.scss

Lines 105 to 106 in d111183

	p {
	margin: 0;

swagger-ui/src/style/_table.scss

Lines 191 to 192 in d111183

	p {
	margin: 0;

which override the default spacing from:

swagger-ui/src/style/_markdown.scss

Lines 1 to 3 in d111183

	.markdown, .renderedMarkdown {
	p, pre {
	margin: 1em auto;

The two abovementioned rules were added in #8214 to fix vertical misalignment of description text compared to other columns.

I think replacing a blanket margin: 0 with a more specific margin-top: 0 applicable only to the 1st paragraph of a block will both fix the paragraph spacing issue AND maintain the fix for #8214.

Motivation and Context

Improve readability of multi-paragraph descriptions.

How Has This Been Tested?

Tested manually by comparing the visual appearance in the online demo (petstore.swagger.io) and in the local build.

Screenshots (if appropriate):

Before	After

Checklist

My PR contains...

• No code changes (src/ is unmodified: changes to documentation, CI, metadata, etc.)
• Dependency changes (any modification to dependencies in package.json)
• Bug fixes (non-breaking change which fixes an issue)
• Improvements (misc. changes to existing features)
• Features (non-breaking change which adds functionality)

My changes...

• are breaking changes to a public API (config options, System API, major UI change, etc).
• are breaking changes to a private API (Redux, component props, utility functions, etc.).
• are breaking changes to a developer API (npm script behavior changes, new dev system dependencies, etc).
• are not breaking changes.

Documentation

• My changes do not require a change to the project documentation.
• My changes require a change to the project documentation.
• If yes to above: I have updated the documentation accordingly.

Automated tests

• My changes can not or do not need to be tested.
• My changes can and should be tested by unit and/or integration tests.
• If yes to above: I have added tests to cover my changes.
• If yes to above: I have taken care to cover edge cases in my tests.
• All new and existing tests passed.