Replace finished_at with deployed_at for Deployment entity

Instead of `finished_at` attribute use `deployed_at` methods which also
takes into account the deployment status.

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/56130.

app/serializers/deployment_entity.rb

@@ -18,7 +18,7 @@ class DeploymentEntity < Grape::Entity
   end
 
   expose :created_at
-  expose :finished_at
+  expose :deployed_at
   expose :tag
   expose :last?
   expose :user, using: UserEntity

app/serializers/deployment_serializer.rb

@@ -4,7 +4,7 @@ class DeploymentSerializer < BaseSerializer
   entity DeploymentEntity
 
   def represent_concise(resource, opts = {})
-    opts[:only] = [:iid, :id, :sha, :created_at, :finished_at, :tag, :last?, :id, ref: [:name]]
+    opts[:only] = [:iid, :id, :sha, :created_at, :deployed_at, :tag, :last?, :id, ref: [:name]]
     represent(resource, opts)
   end
 end

changelogs/unreleased/56130-deployed_at.yml

+---
+title: Replace finished_at with deployed_at for the internal API Deployment entity
+merge_request: 32000
+author:
+type: other

spec/fixtures/api/schemas/deployment.json

@@ -3,7 +3,7 @@
   "required": [
     "sha",
     "created_at",
-    "finished_at",
+    "deployed_at",
     "iid",
     "tag",
     "last?",
@@ -12,7 +12,7 @@
   ],
   "properties": {
     "created_at": { "type": "string" },
-    "finished_at": { "type": ["string", "null"] },
+    "deployed_at": { "type": ["string", "null"] },
     "id": { "type": "integer" },
     "iid": { "type": "integer" },
     "last?": { "type": "boolean" },

spec/serializers/deployment_entity_spec.rb

@@ -32,8 +32,8 @@ describe DeploymentEntity do
     expect(subject).to include(:created_at)
   end
 
-  it 'exposes finished_at' do
-    expect(subject).to include(:finished_at)
+  it 'exposes deployed_at' do
+    expect(subject).to include(:deployed_at)
   end
 
   context 'when the pipeline has another manual action' do