The stable/xena branch has been deleted, so reno can't find its
release notes. Use the xena-eom tag to indicate the end of the
Glance project's maintenance of the Xena series.
This strategy is consistent with the way we handled stable/yoga and
was agreed upon at the 8 Feb Glance meeting:
https://meetings.opendev.org/meetings/glance/2024/glance.2024-02-08-14.00.log.html#l-58
Change-Id: I3473a36a473767531c19463611d3eddb1a676998
Add file to the reno documentation build to show release notes for
stable/xena.
Use pbr instruction to increment the minor version number
automatically so that master versions are higher than the versions on
stable/xena.
Sem-Ver: feature
Change-Id: Idad534678f8e66469b46e293e2aa3d965ff2c9cf