ENH Add config to optionally disable image resampling

[leochenftw]

This is used in silverstripe/silverstripe-asset-admin#1252

[michalkleiner]

Thank you for raising the PR, @leochenftw. I saw the linked PR as well and I think it makes sense to allow for this configuration to be added, even on the File class despite there being Image class as well (which doesn't do much on its own).
I've suggested to reverse the name into a positive form (to reflect what the default is) and that the intention is to allow to optionally turn the resampling off.
If you could force-push an update and also change the commit message to read "ENH Add config to optionally disable image resampling" I'd be happy to merge that.

Thanks!

[michalkleiner]

Thanks for the tweaks @leochenftw. Since this is an enhancement, the PR needs to be based off and target the 1 branch.
Can you please also squash the commits so that it's just a single commit with the message I suggested? I can squash the commits at our end, but I can't rebase the PR.

[leochenftw]

thanks, @michalkleiner , I've rebased it to 1