Return amphora provider back

As Magnum does rely on `amphora` provider as a default and we got
a notice from Octavia devs that `amphora` provider is gonna stay
while potentially `amphorav2` might be sunsetted in the future,
it makes sense to partially revert the [1] and return `amphora` back.

[1] https://review.opendev.org/c/openstack/openstack-ansible-os_octavia/+/885519

Change-Id: Ia34be7a05593b034003bd40c866fbf6561a154e5
(cherry picked from commit 17e0de1112382b2653e4129aea089962d98b32a9)

defaults/main.yml

@@ -492,6 +492,7 @@ octavia_enabled_provider_agents:
   - "{{ (octavia_ovn_enabled | bool) | ternary('ovn', None) }}"
 
 octavia_enabled_provider_drivers:
+  - "amphora:'The Octavia Amphora driver.'"
   - "amphorav2:'The Octavia Amphora v2 driver.'"
   - "{{ (octavia_ovn_enabled | bool) | ternary(\"ovn:'The Octavia OVN provider driver.'\", False) }}"
 octavia_default_provider_driver: "amphorav2"

releasenotes/notes/return_amphora_provider-05deae1d173dbb1f.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    An Octavia ``amphora`` provider was returned back to the list of supported
+    providers to satisfy Magnum ``octavia_provider`` default label.