Use supplied packageName instead of hardcoded

[Katur7]

Hardcoding open_api_utils there breaks this package if packageName option is used for generating the server code.
Use the provided {{packageName}} template variable the same as it is used in the rest of the file.
The samples do not change when using the default packageName.

CC erlang technical committe
@tsloughter @jfacorro @robertoaloi

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project before.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under.\bin\windows) to update Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit, and these must match the expectations made by your contribution. You only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the code or mustache templates for a language ({LANG}) (e.g. php, ruby, python, etc).
• File the PR against the correct branch: master, 4.3.x, 5.0.x. Default: master.
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

[wing328]

@Katur7 thanks for the PR, which looks good to me. I'll merge over the weekend if no one has further questions/feedback.

[Katur7]

Sounds good :)

[Katur7]

@wing328, Hi, is there anything I can do to help getting this merged?

[wing328]

@Katur7 nope, just merged. Sorry for the delay. Thanks again for the contribution.