[BUG][GO] Dependency no longer accessible

Created by: acabarbaye

Description

Current go.mod templates refers to a dependency (oauth2) which no longer exists https://github.com/OpenAPITools/openapi-generator/blob/d19bfebedaa36118483a1b4778a072c6f578bc1e/modules/openapi-generator/src/main/resources/go/go.mod.mustache#L6

See https://pkg.go.dev/golang.org/x/oauth2?tab=versions

Thus, the generated client can no longer build

@wing328 @antihax