Add some scripts to facilitate plugin generation for new ES versions

[Amli]

• prepare-version.sh sets up the environment based on targeted ES version
• build.sh just run gradlew in a docker container

It also adds a github action workflows to run the build and tests.

Next steps would be to:

• replicate this on the other plugin repository
• automate releases

[5k4nd]

I just fixed a small Dockerfile issue preventing from starting the daemon, otherwise it works like a charm, thank you @Amli

I changed the .env file to point to the current master version, hence we can merge in this state after @garaud approval.

[garaud]

Tested locally. Works well. Thanks for this job!

I might be possible with the ./prepare-version.sh to get the pathhierarchy-aggregation-x.y.z.zip in the local build/distributions folder? Or add a sentence to the README file to explain how we can retrieve this file from the container.

[garaud]

works well, thank you!

[Amli]

I might be possible with the ./prepare-version.sh to get the pathhierarchy-aggregation-x.y.z.zip in the local build/distributions folder? Or add a sentence to the README file to explain how we can retrieve this file from the container.

@garaud I changed the README a bit to process more accurate, it was not up to date 🙏