Restore lb_member.yaml template

this is followup to I9cf7532d51843698b63bae2ee825f683f07e2df8

This template file was erroneously deleted, as it is actually still
being used in other existing Octavia tests in
`heat_tempest_plugin.tests.scenario.test_octavia_lbaas`.

Closes-Issue: PRODX-47231
Change-Id: I6743e44f003b67435fd4a32395bfdc87fdef6139
(cherry picked from commit e2a516a45579f8b7330d9c9fe7b87cfbd553e2c4)
1 file changed