fix(core): custom generators help should print relevant information

[meeroslav]

Current Behavior

Running nx workspace-generator custom-name --help prints out the default help for root nx workspace-generator command

Expected Behavior

Running nx workspace-generator custom-name --help should print custom generator specific CLI help

Related Issue(s)

Fixes #12253

cc @rarmatei

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✅ Successfully ran 12 targets

• nx affected --target=e2e --base=65a079cbe134541e541847ab7b25c8ddcbca2a97 --head=86d00b9bb4a9b6da4c397cc845e8d7315cf1f57a --exclude=e2e-storybook,e2e-storybook-angular,e2e-react-native,e2e-detox,e2e-make-angular-cli-faster --parallel=1
• nx affected --target=test --base=65a079cbe134541e541847ab7b25c8ddcbca2a97 --head=86d00b9bb4a9b6da4c397cc845e8d7315cf1f57a --parallel=1
• nx affected --target=build --base=65a079cbe134541e541847ab7b25c8ddcbca2a97 --head=86d00b9bb4a9b6da4c397cc845e8d7315cf1f57a --parallel=3
• nx affected --target=lint --base=65a079cbe134541e541847ab7b25c8ddcbca2a97 --head=86d00b9bb4a9b6da4c397cc845e8d7315cf1f57a --parallel=3
• nx-cloud record -- yarn depcheck
• nx-cloud record -- yarn nx workspace-lint
• nx-cloud record -- yarn check-lock-files
• nx-cloud record -- yarn check-commit
• nx-cloud record -- yarn nx format:check --base=65a079cbe134541e541847ab7b25c8ddcbca2a97 --head=86d00b9bb4a9b6da4c397cc845e8d7315cf1f57a
• nx-cloud record -- yarn check-imports
• nx-cloud record -- yarn documentation
• nx build typedoc-theme

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