[BUG] DefaultCodegen#writeOptional should honor options such as skipOverwrite/codegen ignore

Description

Rules for skipping 50-100 files across a handful of generators is not intuitive.

openapi-generator version

all

Steps to reproduce

• Add any text to samples/openapi3/client/petstore/ruby/spec/spec_helper.rb
• Commit a WIP commit
• Run openapi-generator batch --verbose bin/ci/openapi3-ruby-client-petstore.json
• Notice no diff because the file is silently skipped due to writeOptional
• Run ./bin/openapi3/ruby-client-petstore.sh
• Notice diff because file is deleted in the bash script via:

find samples/openapi3/client/petstore/ruby/spec -type d -not -name spec -not -name custom | xargs rm -Rf
find samples/openapi3/client/petstore/ruby/spec -type f -not -name petstore_helper.rb -not -iwholename '*/spec/custom/*' | xargs rm -Rf

Suggest a fix

Remove support for writeOptional in favor of newer methods for controlling writes. If outputs under samples require these to be unmodified, they should be added to respective .openapi-generator-ignore files.