Improve Gradle scripts

[MGaetan89]

Pull request

Description

Small tweaks to Gradle scripts.

Changes made

• Use Gradle lazy API. Replace calls to create by register. The former immediately creates and configures the object, the latter only does it when needed.
• Only keep English resources in demo applications, since they are not translated anyway. This should help reduce the size of the final application.
• Only creates the nightly flavor on CI.

Checklist

• APIs have been properly documented (if relevant).
• The documentation has been updated (if relevant).
• New unit tests have been written (if relevant).
• The demo has been updated (if relevant).

[github-actions]

Code Coverage

Overall Project	52.09% -0.08%	🟢
Files changed	0%	🟢

Module	Coverage
Kover Gradle Plugin XML report for :plugins	7.19% -1.63%	🟢

Files

Module	File	Coverage
Kover Gradle Plugin XML report for :plugins	PillarboxAndroidApplicationPlugin.kt	0% -11.11%	🟢