docs: add ignore create help

[fsargent]

Summary

• add CLI help docs for snyk ignore create
• mention snyk ignore create from snyk ignore --help
• add focused help acceptance coverage
• add npm run help:audit to programmatically list visible command paths without matching help docs

Test plan

• make format
• make lint
• npm run help:audit
• npx jest --runInBand test/jest/acceptance/help.spec.ts
• npx tap --timeout=300 test/tap/args.test.ts (assertions passed; standalone TAP exits nonzero after coverage output)
• make build BUILD_MODE=public

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[snyk-io]

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