Update PR template to contain all scripts to run (#14501)

* Update PR template to contain all scripts to run

* Makes template more precise

* Avoid requesting to run scripts that are not useful.

Author: jlengrand

.github/PULL_REQUEST_TEMPLATE.md

@@ -16,5 +16,10 @@
   These must match the expectations made by your contribution. 
   You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example `./bin/generate-samples.sh bin/configs/java*`. 
   For Windows users, please run the script in [Git BASH](https://gitforwindows.org/).
+- [ ] In case you are adding a new generator, run the following additional script : 
+  ```
+  ./bin/utils/ensure-up-to-date.sh
+  ``` 
+  Commit all changed files.
 - [ ] File the PR against the [correct branch](https://github.com/OpenAPITools/openapi-generator/wiki/Git-Branches): `master` (6.3.0) (minor release - breaking changes with fallbacks), `7.0.x` (breaking changes without fallbacks)
 - [ ] If your PR is targeting a particular programming language, @mention the [technical committee](https://github.com/openapitools/openapi-generator/#62---openapi-generator-technical-committee) members, so they are more likely to review the pull request.