[designate-tempest-plugin] Tag xena-last

Xena branch is in Extended Maintenance now[1]. Tempest and
tempest plugins are branchless which means master version of
Tempest and its plugins is used to test the supported stable
branches.

Once any stable branch is moved to EM state then, Tempest and
its plugins compatible tag[2] needs to be released so that we can
keep testing the EM stable branches with that tag once master
Tempest and its plugins are not compatible[3].

Tagging 'xena-last' as well as a new version also with same hash.

[1] https://releases.openstack.org/wallaby/index.html
[2] https://docs.openstack.org/tempest/latest/stable_branch_support_policy.html
[3] https://docs.openstack.org/tempest/latest/tempest_and_plugins_compatible_version_policy.html

Change-Id: I90e2f0bfeff36942af14a22c11cc708373fa5076

deliverables/bobcat/designate-tempest-plugin.yaml

@@ -13,3 +13,7 @@ releases:
     projects:
       - repo: openstack/designate-tempest-plugin
         hash: 64cf3eaf108de73dd35d146ef26abb2fb78640d0
+  - version: 0.19.0
+    projects:
+      - repo: openstack/designate-tempest-plugin
+        hash: 25c93a50ec2ce08677129071b123ce056fef9fe5

deliverables/xena/designate-tempest-plugin.yaml

@@ -13,3 +13,7 @@ releases:
     projects:
       - repo: openstack/designate-tempest-plugin
         hash: da27a70ae2b39695ef6f03bbefb55afeacf1cdf3
+  - version: xena-last
+    projects:
+      - repo: openstack/designate-tempest-plugin
+        hash: 25c93a50ec2ce08677129071b123ce056fef9fe5