[oe] RFC: DISTRO_FEED_CONFIGS

[Rod Whitby]

I would like to propose a new standard OE variable called
DISTRO_FEED_CONFIGS which is a list of packages to be installed in a
rootfs to enable the corresponding DISTRO_PACKAGE_MANAGER to actually
access the feeds associated with the distro.  A distro which did not
have feed config packages could leave it as the default empty string and
remain unchanged in the face of this RFC.

This variable would be set in the respective distro.conf, along with
DISTRO_PACKAGE_MANAGER.  It would initially be used in base-image.bb
(see that file for an example of use), and then elsewhere as desired.

For example, in Angstrom, it would replace the existing
ANGSTROM_FEED_CONFIGS variable.

-- Rod