Improve the CI to allow adding new config

[pascalgrimaud]

Following discussion in

• Add Spring Boot LangChain4j sample #11335

We need to improve our CI to allow adding new config.
The workflow should be:

If the app already exists in main branch:
- get md5sum of app in main branch
- get md5sum of app in pull request branch
- compare
    - if it's the same value, stop the CI
    - if it's a different value, launch tests

If the app doesn't exist in main branch
- get md5sum of app in main branch, not exist
- no need to get md5sum of app in pull request branch
- nothing to compare, launch tests

[renanfranca]

I implemented a solution, and I am going to try it out tomorrow morning 👍

Thanks for the complete description of what I need to do.