Improve release instructions

[cbliard]

Is your pull request related to a problem? Please describe.

While releasing Cucumber-JVM 6.6.0, we ran into some issues:

• We (wrongly) assumed that setting the version is done by editing it in the root pom.xml, which made the release process because versions in root pom and submodules pom do not match
• We manually reverted some files and got issues with the update-changelog.sh script
• We were not sure that credentials for pushing artifacts to sonatype would automatically work

Overall the overall release process went smoothly. Anyway we think we can improve it even further.

Describe the solution you have implemented

• Make update-changelog.sh more robust and runnable on osx
• Add information about proper way to set version
• Clarify what credentials information is needed
• Remove empty sections automatically

[coveralls]

Coverage remained the same at 86.198% when pulling d6d49b6 on improve-release-instructions into 26d1ad7 on main.

[cbliard]

I really feel like we could add some unit tests on `scripts/update-changelog.sh. Some kind of golden testing ones where we have input files and expected outputs for many different changelog files would be easy to maintain.

[mpkorstanje]

Looking good!

Don't forget to copy this to:

• https://github.com/cucumber/cucumber-jvm-scala
• https://github.com/cucumber/cucumber-parent

I really feel like we could add some unit tests on `scripts/update-changelog.sh. Some kind of golden testing ones where we have input files and expected outputs for many different changelog files would be easy to maintain.

This script is executed in the docker container so it could be added to the docker image. And as part of building the image some tests could be added. This would also remove the duplication I mentioned above.

The docker image is kept in:

https://github.com/cucumber/cucumber-build

[mpkorstanje]

I think we're good to go now.