GH-348: [Release] Update versions for 16.0.0

[amoeba]

Closes #348

This PR:

• Updates versions from 15.0.0 to 16.0.0
• Updates the R cookbook to pass under 16.0.0
• Updates the C++ cookbook to pass under 16.0.0
• Changes test_cpp_cookbook.yml to now always test against stable libarrow. This is a workaround for not having an up-to-date conda-nightlies channel, see [CI][Packaging] Fix conda arrow-nightlies channel arrow#41856

[amoeba]

@raulcd whenever you have a second can you double-check my thinking here on merging this as-is? This can definitely wait until after other release tasks.

The dev version of the C++ cookbooks have been failing because the conda-nightlies channel is broken. We've talked about what to do here but I dropped the ball on figuring out a solution. In this PR I modified the C++ workflow to just test from the stable channel just so everything passes. Before this PR, it was testing against the nightly channel.

I think this a decent direction to go with for now until the nightlies channel is fixed. Testing the cookbook against the nightlies is still useful IMO so we could restore the change this PR makes when that's resolved.

[raulcd]

I suppose the problem is that main should run against current dev and the stable branch against the latest release instead of a really old release like 16.0.0. I am fine having both run against the latest stable release temporarily while we find how to fix so main runs against dev. At this point I am thinking if building ourselves and or using wheels would be easier than conda nightlies.

I am ok merging this if this is an interim to publish 18.0.0. It is better than what we have already :)
Maybe we should add a note to the README to update or add a disclaimer to this:

See https://arrow.apache.org/cookbook/ for the latest published version using the latest stable version of Apache Arrow. See https://arrow.apache.org/cookbook/dev for the latest published version using the development version of Apache Arrow.

[amoeba]

Thanks @raulcd. Yes this is temporary and I think your suggestion about just having the cookbook repository build what it needs or use wheels makes sense.

[amoeba]

I added a note about the state of the dev cookbooks in 4db967f and will merge this now.

[amoeba]

After merging, locally I ran dev/release/02-update.sh 16.0.0 which updated the stable branch and tagged apache-arrow-16.0.0. There were two commits on stable that weren't on master so I also pushed a backup of stable to https://github.com/amoeba/arrow-cookbook/tree/stable-backup-20241030.