Improve .conda support in conda-build

cep-cb-conda-format.md

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+<table>
+<tr><td> Title </td><td> Improved support for .conda packages in conda-build </td>
+<tr><td> Status </td><td> Proposed </td></tr>
+<tr><td> Author(s) </td><td> Steve Croce &lt;scroce@anaconda.com&gt;</td></tr>
+<tr><td> Created </td><td> Dec 29, 2021</td></tr>
+<tr><td> Updated </td><td> Jan 18, 2022</td></tr>
+<tr><td> Discussion </td><td> NA </td></tr>
+<tr><td> Implementation </td><td> To be implemented </td></tr>
+</table>
+
+## Abstract
+
+The `.conda` package format has been in use within the conda ecosystem for years and has a number of advantages over the `.tar.bz2` format. However, building both `.conda` and `.tar.bz2` packages still requires multiple steps and is not well documented. conda-build should fully support building and outputting `.conda` package formats in addition to the "legacy" `.tar.bz2` format either individually or at the same time.
+
+## Specification
+
+Today, conda-build includes functionality to create `.conda` packages if:
+
+- in a package's meta.yaml, output `type` field set to `conda_v2` *OR*
+- in .condarc, `pkg_format` is set to 2
+
+The proposal is to:
+
+- Expand the `pkg_format` setting in the .condarc to accept a list of formats to build.
+- Expand the conda_build_config.yaml with a setting to provide package format(s) and accept a list of formats.
+- Improve conda-build's documentation for the package format and how to create it
+
+A topic for discussion is whether default behavior should changed at some point to build both `.tar.bz2` and `.conda`, and the appropriate timeline to do so. This could help improve adoption and support of the `.conda` format.
+
+## Reference
+
+    * https://docs.google.com/document/d/1HGKsbg_j69rKXPihhpCb1kNQSE8Iy3yOsUU2x68x8uw/edit
+    * https://github.com/conda/conda/pull/8265
+    * https://github.com/conda/conda-build/pull/3334
+
+## Copyright
+
+All CEPs are explicitly [CC0 1.0 Universal](https://creativecommons.org/publicdomain/zero/1.0/).