ci: build and publish javax flavour

[federicorispo]

The 'release' github action has a new job to build the javax flavour of this project. This job has three main steps:

• Replace all the jakarta imports and dependencies with the javax ones
• Downgrade springframework dependency to the version 5.*
• Using jdk 11 to build the project and publish it

The cold migration from jakarta to javax is done via a new bash script .github/replaceJakartaWithJavax.sh that uses mainly the sed command to perform the replacement operations.

In gradle.properties the SOURCE_COMPATIBILITY and the TARGET_COMPATIBILITY constants are downgraded to 11 in order to allow the users to use the latest version of this library even in projects where the jdk11 is mandatory.

Updated the README with a brief explanation of the difference between the two flavours of this project.

[oliemansm]

@federicorispo Could you merge the two snapshot workflows as well the same way you did with release? So that when a snapshot is published it also publishes one for javax.

[federicorispo]

@oliemansm no problem, I will do it! What about tags? For now there is only one tag for both flavours: is it ok for you?

[oliemansm]

Yeah now that it's on one branch again that sounds ok 👍🏻