Add and update GitHub actions

[Bjorkan]

Quick info

This PR adds one new GitHub action aswell as updates the existing one for releases. Please double check everything before merging anything as I am a "noobie" as it comes to these things, however I have spent yesterday evening testing and everything seems to work!

Add Pull Request Build Action

This commit adds PR.yml which is a GitHub action that will try and build the PR being submitted to make sure it can be built and also to help people beta-testing PR. Hopefully saving everyone time! The built jar files are then uploaded as artifacts of the action in an easy to download .zip file! Uses the gradle build action as seen here to cache gradle between actions: https://github.com/gradle/gradle-build-action

Update release.yml

Makes small adjustment to release.yml file to make the gradle cache it's own thing from the Setup Java, like the action explained above. Uses the gradle build action as seen here to cache gradle between actions: https://github.com/gradle/gradle-build-action

I have not touched the release.yml file as much because I don't fully understand how it works but the small change I made on it should still allow it to work as intended, but testing it would not hurt!

[Bjorkan]

I just found the PR #1 which did almost the same thing as this, and read your comment to him. As such I decided to close this PR and if you decide to use some of this code you are more than welcome but I understand totally your reasoning.

Have a nice day!