fix: add explicit remove assignment actions to macros and automations (#12172)

This updates macros and automations so agents can explicitly remove
assigned agents or teams, while keeping the existing `Assign -> None`
flow working for backward compatibility.

Fixes: #7551
Closes: #7551

## Why
The original macro change exposed unassignment only through `Assign ->
None`, which made macros behave differently from automations and left
the explicit remove actions inconsistent across the product. This keeps
the lower-risk compatibility path and adds the explicit remove actions
requested in review.

## What this change does
- Adds `Remove Assigned Agent` and `Remove Assigned Team` as explicit
actions in macros.
- Adds the same explicit remove actions in automations.
- Keeps `Assign Agent -> None` and `Assign Team -> None` working for
existing behavior and stored payloads.
- Preserves backward compatibility for existing macro and automation
execution payloads.
- Downmerges the latest `develop` and resolves the conflicts while
keeping both the new remove actions and current `develop` behavior.

## Validation
- Verified both remove actions are available and selectable in the macro
editor.
- Verified both remove actions are available and selectable in the
automation builder.
- Applied a disposable macro with `Remove Assigned Agent` and `Remove
Assigned Team` on a real conversation and confirmed both fields were
cleared.
- Applied a disposable macro with `Assign Agent -> None` and `Assign
Team -> None` on a real conversation and confirmed both fields were
still cleared.

spec/controllers/api/v1/accounts/automation_rules_controller_spec.rb

@@ -68,6 +68,12 @@ RSpec.describe 'Api::V1::Accounts::AutomationRulesController', type: :request do
               'action_name': :assign_team,
               'action_params': [1]
             },
+            {
+              'action_name': :remove_assigned_agent
+            },
+            {
+              'action_name': :remove_assigned_team
+            },
             {
               'action_name': :add_label,
               'action_params': %w[support priority_customer]

spec/controllers/api/v1/accounts/macros_controller_spec.rb

@@ -78,6 +78,9 @@ RSpec.describe 'Api::V1::Accounts::MacrosController', type: :request do
               'action_name': :add_label,
               'action_params': %w[support priority_customer]
             },
+            {
+              'action_name': :remove_assigned_agent
+            },
             {
               'action_name': :remove_assigned_team
             },
@@ -484,6 +487,22 @@ RSpec.describe 'Api::V1::Accounts::MacrosController', type: :request do
 
           expect(conversation.reload.team_id).to be_nil
         end
+
+        it 'Unassign the agent' do
+          macro.update!(actions: [
+                          { 'action_name' => 'remove_assigned_agent' }
+                        ])
+          conversation.update!(assignee: user_1)
+          expect(conversation.reload.assignee).to be_present
+
+          perform_enqueued_jobs do
+            post "/api/v1/accounts/#{account.id}/macros/#{macro.id}/execute",
+                 params: { conversation_ids: [conversation.display_id] },
+                 headers: administrator.create_new_auth_token
+          end
+
+          expect(conversation.reload.assignee).to be_nil
+        end
       end
     end
   end