The default for `experimental-features` is not fully enabling CA

[NobbZ]

The current default for experimental-features enables ca-derivations, which enables one to build content addressed derivations, but not to have them as inputs to other derivations, regardless of them beeing CA or IA.

Therefore please also enable ca-references by default.

[blaggacao]

Therefore please also enable ca-references by default.

I'd rather argue for removing anything non-flake related. Other feature flags are orthogonal to this entire repo and people would be rightfully surprised to find them set here.

Thanks for raising the topic!

[NobbZ]

As CA was enabled, I assumed, its actually required for FU+. If this is not the case, I am the same opinion as David, please remove it completely and make it easier for users to add experimental features as suggested in #76.