Conda: use labels for dev releases

[pdiakumis]

See https://www.anaconda.com/docs/tools/anaconda-org/user-guide/work-with-labels

For rattler-build upload looks like the --channel option should do the trick:

rattler-build upload anaconda --help                                                                                                                                                                 <aws:umccr-pro>
Options for uploading to a Anaconda.org server

Usage: rattler-build upload anaconda [OPTIONS] --owner <OWNER> [PACKAGE_FILES]...

Arguments:
  [PACKAGE_FILES]...
          The package file to upload

Options:
  -o, --owner <OWNER>
          The owner of the distribution (e.g. conda-forge or your username)

          [env: ANACONDA_OWNER=]

  -c, --channel <CHANNELS>
          The channel / label to upload the package to (e.g. main / rc)

          [env: ANACONDA_CHANNEL=]

  -a, --api-key <API_KEY>
          The Anaconda API key, if none is provided, the token is read from the keychain / auth-file

          [env: ANACONDA_API_KEY=]