Docs for pre/dev releases

[CJ-Wright]

Following up from #147 it would be nice to have some docs for how to setup/use pre and dev releases. I would suggest having the channel be conda-forge/label/dev_<name_of_package> to match the proposal from conda/conda#8752.

Once this is documented/agreed we can start the bot making dev/pre-release PRs as appropriate. For bot policy discussion see/extend: regro/cf-scripts#86 I think the main concern there is the rate of PRs, maintainer bandwidth, and CI resource availability.

[yarikoptic]

I am looking to provide rc's of datalad. It should be a very straightforward use case AFAIK.
If not proper docs, any hints or pointer to an example feedstock to mimic after, would be greatly appreciated! Everything I found ATM is only initial attempts and probably deprecated by now.

[CJ-Wright]

This was raised as a policy discussion here: conda-forge/cfep#3
Sorry for the bouncing of issue to issue.

[ihnorton]

In case anyone else finds this issue while trying to do a pre-release, here are a few misc issues I encountered; passing along in case it helps someone else.

• if doing a local build of some package with an RC dependency already built on a feedstock, make sure there are NO LOCAL BUILDS in the conda-build/<arch> folder, because that one will be preferred over anything that is an upstream label (and per the next item, can't seem to pin in order to force resolving a newer version from feedstock RC release)
• the documented 1.2.3rc0 version format doesn't seem to work in meta.yaml -- pinning 1.2.* does not resolve. (maybe Fix pinning expressions for prerelease builds conda/conda-build#4272 was intended to fix that, but I have conda-build 3.21.7 which should include that PR, and not working). I had to remove the pin to get the rc package from a dependency build.
  • I was eventually able to get the pinning to work, by using the exact version in conda_build_config.yaml
• (there is (maybe?) some non-determinacy in the re-render process -- after re-rendering multiple times I ended up with a build error on the feedstock 'python_impl' is undefined because that config had been removed; re-rendering again seems to have fixed it)

(working example: branch for tiledb and branch for dependee tiledb-py building against the tiledb_rc label -- linked compare view there to avoid cruft commits in the process of getting it to build)