[REQ][repo] Use CODEOWNERS

Is your feature request related to a problem? Please describe.

The PR Checklist states

Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

This step can be automated using CODEOWNERS making it easier for everyone 👯‍♂

Describe the solution you'd like

By placing CODEOWNERS file in the .github folder language specific people/teams can be auto assigned to review PRs in their field of expertise.

Here's an example/start

# Core
/modules/* @OpenAPITools/generator-core-team
/modules/openapi-generator-cli/ @OpenAPITools/generator-core-team
/modules/openapi-generator-core/ @OpenAPITools/generator-core-team
/modules/openapi-generator-gradle-plugin/ @OpenAPITools/generator-core-team
/modules/openapi-generator-maven-plugin/ @OpenAPITools/generator-core-team
/modules/openapi-generator-online/ @OpenAPITools/generator-core-team

# TypeScript Clients
## folders
**/*typescript*/** @TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @nicokoenig @topce @akehir
## files
**/*TypeScript* @TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @nicokoenig @topce @akehir
**/*typescript* @TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @nicokoenig @topce @akehir

Additional context

I don't have access to https://github.com/OpenAPITools/teams so I can't tell if each language or client have a separate team. If there is then it might be a good idea to use them.

I also don't know to whom every file should be assigned so I have assumed that files and folders called something with {LANG} belongs to the respective technical committee, everything else is Core.

Start by reviewing the PR Checklist and GitHub's CODEOWNERS behavior. Create the proposed CODEOWNERS file in .github, first confirming which language and core teams are available and which paths they own. Done means pull requests are automatically assigned to the appropriate reviewers without the manual checklist step.