make --ccache on by default

[Be-ing]

Checklist

• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Suggestion

Passing --ccache is very helpful for development and it's annoying to ensure that it is passed to every invocation of flatpak-builder. It would be nice to have it on by default, or some other means of persistently enabling it (environment variable? AFAIK flatpak-builder has no persistent configuration file).

[Erick555]

Changing default will affect everyone who rely on current behavior - ccache not being enabled. I think default shouldn't be changed.

[tbertels]

Something that could be done is add a command to disable ccache (like --no-ccache) and show a warning when neither --ccache nor the new command has been used, stating that in the future ccache will enabled by default.

Then some time in the future, enable ccache by default while still keeping the warning.