Use latest Magepack version by default

[sprankhub]

Warden by default uses a very old Magepack version:

warden/environments/magento2/magento2.magepack.base.yml

Line 5 in 9548566

image: ${WARDEN_IMAGE_REPOSITORY}/magepack:${MAGEPACK_VERSION:-2.3}

We should at least propose using the newest version in the example .env file (if not bumping the default version).

[ihor-sviziev]

@sprankhub don't you think that the default value should be also updated?

[sprankhub]

@ihor-sviziev, I personally think so (I even suggested it above), but this would be kind of a breaking change 🤔

[navarr]

@ihor-sviziev @sprankhub It's a difficult question, which is why I've erred on the side of leaving it alone (for now).

I think at this point, nobody using Warden is expecting an undefined Magepack version to be the latest version. Such a change would really only benefit new users, while possibly being an unexpected change for older users.