fix: Code generated in go should have a line that matches Code generated .* DO NOT EDIT.

[jensravn]

PR checklist

• [x] Read the contribution guidelines.
• [ ] Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• [x] Filed the PR against the correct branch: 3.0.0 branch for changes related to OpenAPI spec 3.0. Default: master.
• [ ] Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

Code generated in go should have a line that matches the following regular expression (in Go syntax):

^// Code generated .* DO NOT EDIT\.$

Described here https://pkg.go.dev/cmd/go#hdr-Generate_Go_files_by_processing_source

This will allow other tools that parses go code to treat it as generated code.

An example of this is go's deadcode tool that have the flag -generated to indicate whether it should report on generated code. By default it will skip generated code. https://pkg.go.dev/golang.org/x/tools/internal/cmd/deadcode