debian/control: add osmo-bts meta-package
debian/control: add osmo-bts meta-package

Add an osmo-bts meta-package that depends on the subpackages
osmo-bts-trx and osmo-bts-virtual. This is important, because the
downstream packaging of debian does not split osmo-bts in subpackages,
it has only one osmo-bts package. So without this, when installing
"osmo-bts" in debian while having the Osmocom binary package repository
installed and expecting to get the newer version, the user will actually
get the older version from debian.

Closes: OS#5319
Related: https://salsa.debian.org/debian-mobcom-team/osmo-bts/-/blob/master/debian/control
Change-Id: I1a6edf2eb146616ac51b7957368a8d057caa685f

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts