Adds the alias for jest tests

What does this MR do?

This MR adds an alias for our jest test files. This mirrors the one we currently have for karma.

'../../../../spec/frontend/monitoring/mock_data' becomes 'jest/monitoring/mock_data'

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #196877 (closed)