docs: remaining unaddressed pages for docs-v2 overhaul

[jfy133]

The following pages have not been migrated, replaced, or been official marked for deprecation:

Writing modules/components tutorial-like pages

• https://nf-co.re/docs/tutorials/nf-core_training/writing-nf-core-modules/chapter-1-introduction (and companion pages)
• https://nf-co.re/docs/tutorials/nf-core_components/components
  • Note: it is more detailed that https://docs-v2--nf-core-docs.netlify.app/docs/developing/components/creating-components, but not as detailed as https://nf-co.re/docs/tutorials/nf-core_training/writing-nf-core-modules/chapter-1-introduction

Test related pages

• https://nf-co.re/docs/contributing/nf-test/assertions
• https://nf-co.re/docs/tutorials/tests_and_test_data/nf-test_comprehensive_guide (and companion pages)
• https://nf-co.re/docs/tutorials/tests_and_test_data/test_data
  • Half-superseded by the specifications documentation: https://docs-v2--nf-core-docs.netlify.app/docs/specifications/test-data/overview but has additional field-specific guidance