chore(deps): bump @nestjs/core and @openapitools/openapi-generator-cli

Removes [@nestjs/core](https://github.com/nestjs/nest). It's no longer used after updating ancestor dependency [@openapitools/openapi-generator-cli](https://github.com/OpenAPITools/openapi-generator-cli). These dependencies need to be updated together.


Removes `@nestjs/core`

Updates `@openapitools/openapi-generator-cli` from 2.5.1 to 2.6.0
- [Release notes](https://github.com/OpenAPITools/openapi-generator-cli/releases)
- [Changelog](https://github.com/OpenAPITools/openapi-generator-cli/blob/master/.releaserc)
- [Commits](OpenAPITools/openapi-generator-cli@v2.5.1...v2.6.0)

---
updated-dependencies:
- dependency-name: "@nestjs/core"
  dependency-type: indirect
- dependency-name: "@openapitools/openapi-generator-cli"
  dependency-type: direct:production
...

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