Mark required fields with `required` and `aria-required` attributes

📖 What does this MR do?

Related to #294436 (closed)

Improves a11y and how a screen reader announces the create project pages. Adds required and aria-required attributes to required fields on "Create blank project" and "Import an exported GitLab project" pages

💻 Local testing

1. Navigate to projects/new#blank_project or /import/gitlab_project/new?namespace_id=1&name=&path=
2. Turn on VoiceOver (⌘ + F5)
3. Use Tab to navigate through the fields

📹 Videos

Safari w/ VoiceOver

View	Before	After
Create project	Screen_Recording_2021-03-04_at_9.51.49_AM	Screen_Recording_2021-03-04_at_9.45.28_AM
Import GitLab project	Screen_Recording_2021-03-04_at_9.53.02_AM	Screen_Recording_2021-03-04_at_9.48.02_AM

🚦 Does this MR meet the acceptance criteria?

Conformity

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• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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