Allow margin bottom to be configured on the table component

[AshGDS]

What / Why

• Adds a margin_bottom option to the table component
• This is needed so that we can set the margin_bottom to 0 where this component is nested within another component (as parent components should control all of the margin_bottom, not child components that render inside them)
• Usually we would add the component wrapper helper to achieve this, as that helper includes margin_bottom functionality, but here that isn't easy due to how the component is architected. Therefore, I've added setting margin bottom as it's own option to the component.
• This is a pre requisite to completing this trello card: https://trello.com/c/Q4quM0zo/500-fix-calendar-component-margin
• Test link: https://components-gem-pr-4638.herokuapp.com/component-guide/table/with_custom_margin_bottom

Visual Changes

None - though I've added a new example in the docs, so there is a visual change in Percy.

[JamesCGDS]

LGTM, nice work 👍 FYI I added a commit to the end because I spotted some unrelated typos in the table component docs and thought it'd be quicker for me to fix them whilst I was there