ci: improve links checking

[mdonadoni]

Links in the documentation pages are currently checked using awesome_bot

docs.reana.io/run-tests.sh

Lines 19 to 22 in d904bcd

	check_docstyle () {
	npx -p markdownlint-cli markdownlint docs/*
	awesome_bot --allow-dupe --skip-save-results --allow-redirect docs/**/*.md
	}

However, not all pages are being checked (from these logs):

Summary
   docs/administration/index.md: ✓
   docs/advanced-usage/index.md: ✓
  docs/getting-started/index.md: ✓
        docs/reference/index.md: ✓
docs/running-notebooks/index.md: ✓
docs/running-workflows/index.md: ✓

We might also consider switching to another tool, given that awesome_bot does not check internal relative links between different documentation pages